diff --git a/fastfield_codecs/src/bitpacked.rs b/fastfield_codecs/src/bitpacked.rs
new file mode 100644
index 000000000..ecdd60a73
--- /dev/null
+++ b/fastfield_codecs/src/bitpacked.rs
@@ -0,0 +1,187 @@
+use crate::CodecId;
+use crate::FastFieldDataAccess;
+use crate::FastFieldSerializerEstimate;
+use crate::FastFieldStats;
+use common::BinarySerializable;
+use std::io::{self, Write};
+use tantivy_bitpacker::compute_num_bits;
+use tantivy_bitpacker::BitPacker;
+
+use tantivy_bitpacker::BitUnpacker;
+
+/// Depending on the field type, a different
+/// fast field is required.
+#[derive(Clone)]
+pub struct BitpackedFastFieldReader {
+    bit_unpacker: BitUnpacker,
+    pub min_value_u64: u64,
+    pub max_value_u64: u64,
+}
+
+impl<'data> BitpackedFastFieldReader {
+    /// Opens a fast field given a file.
+    pub fn open_from_bytes(bytes: &[u8]) -> io::Result<Self> {
+        let (_data, mut footer) = bytes.split_at(bytes.len() - 16);
+        let min_value = u64::deserialize(&mut footer)?;
+        let amplitude = u64::deserialize(&mut footer)?;
+        let max_value = min_value + amplitude;
+        let num_bits = compute_num_bits(amplitude);
+        let bit_unpacker = BitUnpacker::new(num_bits);
+        Ok(BitpackedFastFieldReader {
+            min_value_u64: min_value,
+            max_value_u64: max_value,
+            bit_unpacker,
+        })
+    }
+    pub fn get_u64(&self, doc: u64, data: &[u8]) -> u64 {
+        self.min_value_u64 + self.bit_unpacker.get(doc, &data)
+    }
+}
+pub struct BitpackedFastFieldSerializer<'a, W: 'a + Write> {
+    bit_packer: BitPacker,
+    write: &'a mut W,
+    min_value: u64,
+    amplitude: u64,
+    num_bits: u8,
+}
+
+impl<'a, W: Write> BitpackedFastFieldSerializer<'a, W> {
+    /// Creates a new fast field serializer.
+    ///
+    /// The serializer in fact encode the values by bitpacking
+    /// `(val - min_value)`.
+    ///
+    /// It requires a `min_value` and a `max_value` to compute
+    /// compute the minimum number of bits required to encode
+    /// values.
+    pub fn open(
+        write: &'a mut W,
+        min_value: u64,
+        max_value: u64,
+    ) -> io::Result<BitpackedFastFieldSerializer<'a, W>> {
+        assert!(min_value <= max_value);
+        let amplitude = max_value - min_value;
+        let num_bits = compute_num_bits(amplitude);
+        let bit_packer = BitPacker::new();
+        Ok(BitpackedFastFieldSerializer {
+            bit_packer,
+            write,
+            min_value,
+            amplitude,
+            num_bits,
+        })
+    }
+    /// Creates a new fast field serializer.
+    ///
+    /// The serializer in fact encode the values by bitpacking
+    /// `(val - min_value)`.
+    ///
+    /// It requires a `min_value` and a `max_value` to compute
+    /// compute the minimum number of bits required to encode
+    /// values.
+    pub fn create(
+        write: &'a mut W,
+        _fastfield_accessor: &impl FastFieldDataAccess,
+        stats: FastFieldStats,
+        data_iter: impl Iterator<Item = u64>,
+    ) -> io::Result<()> {
+        let mut serializer = Self::open(write, stats.min_value, stats.max_value)?;
+
+        for val in data_iter {
+            serializer.add_val(val)?;
+        }
+        serializer.close_field()?;
+
+        Ok(())
+    }
+    /// Pushes a new value to the currently open u64 fast field.
+    #[inline]
+    pub fn add_val(&mut self, val: u64) -> io::Result<()> {
+        let val_to_write: u64 = val - self.min_value;
+        self.bit_packer
+            .write(val_to_write, self.num_bits, &mut self.write)?;
+        Ok(())
+    }
+    pub fn close_field(mut self) -> io::Result<()> {
+        self.bit_packer.close(&mut self.write)?;
+        self.min_value.serialize(&mut self.write)?;
+        self.amplitude.serialize(&mut self.write)?;
+        Ok(())
+    }
+}
+
+impl<'a, W: 'a + Write> FastFieldSerializerEstimate for BitpackedFastFieldSerializer<'a, W> {
+    fn estimate(
+        _fastfield_accessor: &impl FastFieldDataAccess,
+        stats: FastFieldStats,
+    ) -> (f32, &'static str) {
+        let amplitude = stats.max_value - stats.min_value;
+        let num_bits = compute_num_bits(amplitude);
+        let num_bits_uncompressed = 64;
+        let ratio = num_bits as f32 / num_bits_uncompressed as f32;
+        let name = Self::NAME;
+        (ratio, name)
+    }
+}
+impl<'a, W: 'a + Write> CodecId for BitpackedFastFieldSerializer<'_, W> {
+    const NAME: &'static str = "Bitpacked";
+    const ID: u8 = 1;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn create_and_validate(data: &[u64]) {
+        let mut out = vec![];
+        BitpackedFastFieldSerializer::create(
+            &mut out,
+            &data,
+            crate::tests::stats_from_vec(&data),
+            data.iter().cloned(),
+        )
+        .unwrap();
+
+        let reader = BitpackedFastFieldReader::open_from_bytes(&out).unwrap();
+        for (doc, val) in data.iter().enumerate() {
+            assert_eq!(reader.get_u64(doc as u64, &out), *val);
+        }
+    }
+
+    #[test]
+    fn bitpacked_fast_field_test_simple() {
+        let data = (10..=20_u64).collect::<Vec<_>>();
+
+        create_and_validate(&data);
+    }
+
+    #[test]
+    fn bitpacked_fast_field_test_with_offset() {
+        //let data = vec![5, 50, 95, 96, 97, 98, 99, 100];
+        let mut data = vec![5, 6, 7, 8, 9, 10, 99, 100];
+        create_and_validate(&data);
+
+        data.reverse();
+        create_and_validate(&data);
+    }
+    #[test]
+    fn bitpacked_fast_field_test_no_structure() {
+        let mut data = vec![5, 50, 3, 13, 1, 1000, 35];
+        create_and_validate(&data);
+
+        data.reverse();
+        create_and_validate(&data);
+    }
+    #[test]
+    fn bitpacked_fast_field_rand() {
+        for _ in 0..500 {
+            let mut data = (0..1 + rand::random::<u8>() as usize)
+                .map(|_| rand::random::<i64>() as u64 / 2 as u64)
+                .collect::<Vec<_>>();
+            create_and_validate(&data);
+
+            data.reverse();
+            create_and_validate(&data);
+        }
+    }
+}
diff --git a/fastfield_codecs/src/bitpacked/mod.rs b/fastfield_codecs/src/bitpacked/mod.rs
deleted file mode 100644
index 9dba9f32e..000000000
--- a/fastfield_codecs/src/bitpacked/mod.rs
+++ /dev/null
@@ -1,5 +0,0 @@
-mod reader;
-mod serialize;
-
-pub use reader::BitpackedFastFieldReader;
-pub use serialize::BitpackedFastFieldSerializer;
diff --git a/fastfield_codecs/src/bitpacked/reader.rs b/fastfield_codecs/src/bitpacked/reader.rs
deleted file mode 100644
index 966c9dc44..000000000
--- a/fastfield_codecs/src/bitpacked/reader.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-use common::BinarySerializable;
-use std::io;
-use tantivy_bitpacker::compute_num_bits;
-use tantivy_bitpacker::BitUnpacker;
-/// Depending on the field type, a different
-/// fast field is required.
-#[derive(Clone)]
-pub struct BitpackedFastFieldReader<'data> {
-    bytes: &'data [u8],
-    bit_unpacker: BitUnpacker,
-    pub min_value_u64: u64,
-    pub max_value_u64: u64,
-}
-
-impl<'data> BitpackedFastFieldReader<'data> {
-    /// Opens a fast field given a file.
-    pub fn open_from_bytes(mut bytes: &'data [u8]) -> io::Result<Self> {
-        let min_value = u64::deserialize(&mut bytes)?;
-        let amplitude = u64::deserialize(&mut bytes)?;
-        let max_value = min_value + amplitude;
-        let num_bits = compute_num_bits(amplitude);
-        let bit_unpacker = BitUnpacker::new(num_bits);
-        Ok(BitpackedFastFieldReader {
-            bytes,
-            min_value_u64: min_value,
-            max_value_u64: max_value,
-            bit_unpacker,
-        })
-    }
-    pub fn get_u64(&self, doc: u64) -> u64 {
-        self.min_value_u64 + self.bit_unpacker.get(doc, &self.bytes)
-    }
-}
diff --git a/fastfield_codecs/src/bitpacked/serialize.rs b/fastfield_codecs/src/bitpacked/serialize.rs
deleted file mode 100644
index 40b74ea1d..000000000
--- a/fastfield_codecs/src/bitpacked/serialize.rs
+++ /dev/null
@@ -1,93 +0,0 @@
-use crate::FastFieldDataAccess;
-use crate::FastFieldSerializerEstimate;
-use crate::FastFieldStats;
-use common::BinarySerializable;
-use std::io::{self, Write};
-use tantivy_bitpacker::compute_num_bits;
-use tantivy_bitpacker::BitPacker;
-
-pub struct BitpackedFastFieldSerializer<'a, W: 'a + Write> {
-    bit_packer: BitPacker,
-    write: &'a mut W,
-    min_value: u64,
-    num_bits: u8,
-}
-
-impl<'a, W: Write> BitpackedFastFieldSerializer<'a, W> {
-    /// Creates a new fast field serializer.
-    ///
-    /// The serializer in fact encode the values by bitpacking
-    /// `(val - min_value)`.
-    ///
-    /// It requires a `min_value` and a `max_value` to compute
-    /// compute the minimum number of bits required to encode
-    /// values.
-    pub fn open(
-        write: &'a mut W,
-        min_value: u64,
-        max_value: u64,
-    ) -> io::Result<BitpackedFastFieldSerializer<'a, W>> {
-        assert!(min_value <= max_value);
-        min_value.serialize(write)?;
-        let amplitude = max_value - min_value;
-        amplitude.serialize(write)?;
-        let num_bits = compute_num_bits(amplitude);
-        let bit_packer = BitPacker::new();
-        Ok(BitpackedFastFieldSerializer {
-            bit_packer,
-            write,
-            min_value,
-            num_bits,
-        })
-    }
-    /// Creates a new fast field serializer.
-    ///
-    /// The serializer in fact encode the values by bitpacking
-    /// `(val - min_value)`.
-    ///
-    /// It requires a `min_value` and a `max_value` to compute
-    /// compute the minimum number of bits required to encode
-    /// values.
-    pub fn create(
-        write: &'a mut W,
-        _fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-        data_iter: impl Iterator<Item = u64>,
-    ) -> io::Result<()> {
-        let mut serializer = Self::open(write, stats.min_value, stats.max_value)?;
-
-        for val in data_iter {
-            serializer.add_val(val)?;
-        }
-        serializer.close_field()?;
-
-        Ok(())
-    }
-    /// Pushes a new value to the currently open u64 fast field.
-    pub fn add_val(&mut self, val: u64) -> io::Result<()> {
-        let val_to_write: u64 = val - self.min_value;
-        self.bit_packer
-            .write(val_to_write, self.num_bits, &mut self.write)?;
-        Ok(())
-    }
-    pub fn close_field(mut self) -> io::Result<()> {
-        self.bit_packer.close(&mut self.write)
-    }
-}
-
-impl<'a, W: 'a + Write> FastFieldSerializerEstimate for BitpackedFastFieldSerializer<'a, W> {
-    fn estimate(
-        _fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-    ) -> (f32, &'static str) {
-        let amplitude = stats.max_value - stats.min_value;
-        let num_bits = compute_num_bits(amplitude);
-        let num_bits_uncompressed = 64;
-        let ratio = num_bits as f32 / num_bits_uncompressed as f32;
-        let name = Self::codec_id().0;
-        (ratio, name)
-    }
-    fn codec_id() -> (&'static str, u8) {
-        ("Bitpacked", 1)
-    }
-}
diff --git a/fastfield_codecs/src/lib.rs b/fastfield_codecs/src/lib.rs
index 83a310488..659bb02f6 100644
--- a/fastfield_codecs/src/lib.rs
+++ b/fastfield_codecs/src/lib.rs
@@ -35,8 +35,15 @@ pub trait FastFieldSerializerEstimate {
         fastfield_accessor: &impl FastFieldDataAccess,
         stats: FastFieldStats,
     ) -> (f32, &'static str);
-    /// the unique (name, id) of the compressor. Used to distinguish when de/serializing.
-    fn codec_id() -> (&'static str, u8);
+}
+
+/// `CodecId` is required by each Codec.
+///
+/// It needs to provide a unique name and id, which is
+/// used for debugging and de/serialization.
+pub trait CodecId {
+    const NAME: &'static str;
+    const ID: u8;
 }
 
 #[derive(Debug, Clone)]
@@ -45,3 +52,15 @@ pub struct FastFieldStats {
     pub max_value: u64,
     pub num_vals: u64,
 }
+
+impl<'a> FastFieldDataAccess for &'a [u64] {
+    fn get(&self, doc: u32) -> u64 {
+        self[doc as usize]
+    }
+}
+
+impl FastFieldDataAccess for Vec<u64> {
+    fn get(&self, doc: u32) -> u64 {
+        self[doc as usize]
+    }
+}
diff --git a/fastfield_codecs/src/linearinterpol.rs b/fastfield_codecs/src/linearinterpol.rs
new file mode 100644
index 000000000..759a7d2f3
--- /dev/null
+++ b/fastfield_codecs/src/linearinterpol.rs
@@ -0,0 +1,232 @@
+use crate::CodecId;
+use crate::FastFieldDataAccess;
+use crate::FastFieldSerializerEstimate;
+use crate::FastFieldStats;
+use std::io::{self, Read, Write};
+use tantivy_bitpacker::compute_num_bits;
+use tantivy_bitpacker::BitPacker;
+
+use common::BinarySerializable;
+use common::FixedSize;
+use tantivy_bitpacker::BitUnpacker;
+
+/// Depending on the field type, a different
+/// fast field is required.
+#[derive(Clone)]
+pub struct LinearinterpolFastFieldReader {
+    bit_unpacker: BitUnpacker,
+    pub footer: LinearInterpolFooter,
+    pub slope: f64,
+}
+
+#[derive(Clone, Debug)]
+pub struct LinearInterpolFooter {
+    pub relative_max_value: u64,
+    pub offset: u64,
+    pub first_val: u64,
+    pub last_val: u64,
+    pub num_vals: u64,
+}
+
+impl BinarySerializable for LinearInterpolFooter {
+    fn serialize<W: Write>(&self, write: &mut W) -> io::Result<()> {
+        self.relative_max_value.serialize(write)?;
+        self.offset.serialize(write)?;
+        self.first_val.serialize(write)?;
+        self.last_val.serialize(write)?;
+        self.num_vals.serialize(write)?;
+        Ok(())
+    }
+
+    fn deserialize<R: Read>(reader: &mut R) -> io::Result<LinearInterpolFooter> {
+        Ok(LinearInterpolFooter {
+            relative_max_value: u64::deserialize(reader)?,
+            offset: u64::deserialize(reader)?,
+            first_val: u64::deserialize(reader)?,
+            last_val: u64::deserialize(reader)?,
+            num_vals: u64::deserialize(reader)?,
+        })
+    }
+}
+
+impl FixedSize for LinearInterpolFooter {
+    const SIZE_IN_BYTES: usize = 40;
+}
+
+impl LinearinterpolFastFieldReader {
+    /// Opens a fast field given a file.
+    pub fn open_from_bytes(bytes: &[u8]) -> io::Result<Self> {
+        let (_data, mut footer) = bytes.split_at(bytes.len() - LinearInterpolFooter::SIZE_IN_BYTES);
+        let footer = LinearInterpolFooter::deserialize(&mut footer)?;
+        //let rel_max_value = u64::deserialize(&mut footer)?;
+        //let offset = u64::deserialize(&mut footer)?;
+        //let first_value = u64::deserialize(&mut footer)?;
+        //let last_value = u64::deserialize(&mut footer)?;
+        //let num_vals = u64::deserialize(&mut footer)?;
+        let slope = (footer.last_val as f64 - footer.first_val as f64)
+            / (footer.num_vals as u64 - 1) as f64;
+
+        let num_bits = compute_num_bits(footer.relative_max_value);
+        let bit_unpacker = BitUnpacker::new(num_bits);
+        Ok(LinearinterpolFastFieldReader {
+            footer,
+            bit_unpacker,
+            slope,
+        })
+    }
+    pub fn get_u64(&self, doc: u64, data: &[u8]) -> u64 {
+        let calculated_value = self.footer.first_val + (doc as f64 * self.slope) as u64;
+        (calculated_value + self.bit_unpacker.get(doc, &data)) - self.footer.offset
+    }
+}
+
+/// Fastfield serializer, which tries to guess values by linear interpolation
+/// and stores the difference bitpacked.
+pub struct LinearInterpolFastFieldSerializer {}
+
+// TODO not suitable if max is larger than i64::MAX / 2
+
+impl LinearInterpolFastFieldSerializer {
+    /// Creates a new fast field serializer.
+    pub fn create(
+        write: &mut impl Write,
+        fastfield_accessor: &impl FastFieldDataAccess,
+        stats: FastFieldStats,
+        data_iter: impl Iterator<Item = u64>,
+        data_iter1: impl Iterator<Item = u64>,
+        data_iter2: impl Iterator<Item = u64>,
+    ) -> io::Result<()> {
+        assert!(stats.min_value <= stats.max_value);
+
+        let first_val = fastfield_accessor.get(0);
+        let last_val = fastfield_accessor.get(stats.num_vals as u32 - 1);
+        let slope = get_slope(first_val, last_val, stats.num_vals);
+        // todo walk over data just once and calulate offset on the fly
+        // offset to ensure all values are positive
+        let offset = data_iter1
+            .enumerate()
+            .map(|(pos, val)| {
+                let calculated_value = first_val + (pos as f64 * slope) as u64;
+                val as i64 - calculated_value as i64
+            })
+            .min()
+            .unwrap()
+            .abs() as u64;
+
+        //calc new max
+        let rel_max = data_iter2
+            .enumerate()
+            .map(|(pos, val)| {
+                let calculated_value = first_val + (pos as f64 * slope) as u64;
+                (val + offset) - calculated_value
+            })
+            .max()
+            .unwrap();
+
+        let amplitude = rel_max;
+        let num_bits = compute_num_bits(amplitude);
+        let mut bit_packer = BitPacker::new();
+        for (pos, val) in data_iter.enumerate() {
+            let calculated_value = first_val + (pos as f64 * slope) as u64;
+            let diff = (val + offset) - calculated_value;
+            bit_packer.write(diff, num_bits, write)?;
+        }
+        bit_packer.close(write)?;
+
+        let footer = LinearInterpolFooter {
+            relative_max_value: amplitude,
+            offset,
+            first_val,
+            last_val,
+            num_vals: stats.num_vals,
+        };
+        footer.serialize(write)?;
+        Ok(())
+    }
+}
+fn get_slope(first_val: u64, last_val: u64, num_vals: u64) -> f64 {
+    (last_val as f64 - first_val as f64) / (num_vals as u64 - 1) as f64
+}
+
+impl FastFieldSerializerEstimate for LinearInterpolFastFieldSerializer {
+    fn estimate(
+        _fastfield_accessor: &impl FastFieldDataAccess,
+        stats: FastFieldStats,
+    ) -> (f32, &'static str) {
+        let amplitude = stats.max_value - stats.min_value;
+        let num_bits = compute_num_bits(amplitude);
+        let num_bits_uncompressed = 64;
+        let ratio = num_bits as f32 / num_bits_uncompressed as f32;
+        let name = Self::NAME;
+        (ratio, name)
+    }
+}
+
+impl CodecId for LinearInterpolFastFieldSerializer {
+    const NAME: &'static str = "LinearInterpol";
+    const ID: u8 = 2;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn create_and_validate(data: &[u64]) -> (u64, u64) {
+        let mut out = vec![];
+        LinearInterpolFastFieldSerializer::create(
+            &mut out,
+            &data,
+            crate::tests::stats_from_vec(&data),
+            data.iter().cloned(),
+            data.iter().cloned(),
+            data.iter().cloned(),
+        )
+        .unwrap();
+
+        let reader = LinearinterpolFastFieldReader::open_from_bytes(&out).unwrap();
+        for (doc, val) in data.iter().enumerate() {
+            assert_eq!(reader.get_u64(doc as u64, &out), *val);
+        }
+        (reader.footer.relative_max_value, reader.footer.offset)
+    }
+
+    #[test]
+    fn linear_interpol_fast_field_test_simple() {
+        let data = (10..=20_u64).collect::<Vec<_>>();
+
+        let (rel_max_value, offset) = create_and_validate(&data);
+
+        assert_eq!(offset, 0);
+        assert_eq!(rel_max_value, 0);
+    }
+
+    #[test]
+    fn linear_interpol_fast_field_test_with_offset() {
+        //let data = vec![5, 50, 95, 96, 97, 98, 99, 100];
+        let mut data = vec![5, 6, 7, 8, 9, 10, 99, 100];
+        create_and_validate(&data);
+
+        data.reverse();
+        create_and_validate(&data);
+    }
+    #[test]
+    fn linear_interpol_fast_field_test_no_structure() {
+        let mut data = vec![5, 50, 3, 13, 1, 1000, 35];
+        create_and_validate(&data);
+
+        data.reverse();
+        create_and_validate(&data);
+    }
+    #[test]
+    fn linear_interpol_fast_field_rand() {
+        for _ in 0..500 {
+            let mut data = (0..1 + rand::random::<u8>() as usize)
+                .map(|_| rand::random::<i64>() as u64 / 2 as u64)
+                .collect::<Vec<_>>();
+            create_and_validate(&data);
+
+            data.reverse();
+            create_and_validate(&data);
+        }
+    }
+}
diff --git a/fastfield_codecs/src/linearinterpol/mod.rs b/fastfield_codecs/src/linearinterpol/mod.rs
deleted file mode 100644
index 60d9f1e6e..000000000
--- a/fastfield_codecs/src/linearinterpol/mod.rs
+++ /dev/null
@@ -1,123 +0,0 @@
-mod serialize;
-
-use common::BinarySerializable;
-use std::io;
-use tantivy_bitpacker::compute_num_bits;
-use tantivy_bitpacker::BitUnpacker;
-
-use crate::FastFieldDataAccess;
-/// Depending on the field type, a different
-/// fast field is required.
-#[derive(Clone)]
-pub struct LinearinterpolFastFieldReader<'data> {
-    bytes: &'data [u8],
-    bit_unpacker: BitUnpacker,
-    pub first_value: u64,
-    pub rel_max_value: u64,
-    pub offset: u64,
-    pub slope: f64,
-}
-
-impl<'data> LinearinterpolFastFieldReader<'data> {
-    /// Opens a fast field given a file.
-    pub fn open_from_bytes(mut bytes: &'data [u8]) -> io::Result<Self> {
-        let rel_max_value = u64::deserialize(&mut bytes)?;
-        let offset = u64::deserialize(&mut bytes)?;
-        let first_value = u64::deserialize(&mut bytes)?;
-        let last_value = u64::deserialize(&mut bytes)?;
-        let num_vals = u64::deserialize(&mut bytes)?;
-        let slope = (last_value as f64 - first_value as f64) / (num_vals as u64 - 1) as f64;
-
-        let num_bits = compute_num_bits(rel_max_value);
-        let bit_unpacker = BitUnpacker::new(num_bits);
-        Ok(LinearinterpolFastFieldReader {
-            bytes,
-            first_value,
-            rel_max_value,
-            offset,
-            bit_unpacker,
-            slope,
-        })
-    }
-    pub fn get_u64(&self, doc: u64) -> u64 {
-        let calculated_value = self.first_value + (doc as f64 * self.slope) as u64;
-        calculated_value + self.bit_unpacker.get(doc, &self.bytes) - self.offset
-
-        //self.offset + self.min_value + self.bit_unpacker.get(doc, &self.bytes)
-    }
-}
-
-impl<'a> FastFieldDataAccess for &'a [u64] {
-    fn get(&self, doc: u32) -> u64 {
-        self[doc as usize]
-    }
-}
-
-impl FastFieldDataAccess for Vec<u64> {
-    fn get(&self, doc: u32) -> u64 {
-        self[doc as usize]
-    }
-}
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    fn create_and_validate(data: &[u64]) -> (u64, u64) {
-        let mut out = vec![];
-        serialize::LinearInterpolFastFieldSerializer::create(
-            &mut out,
-            &data,
-            crate::tests::stats_from_vec(&data),
-            data.iter().cloned(),
-            data.iter().cloned(),
-            data.iter().cloned(),
-        )
-        .unwrap();
-
-        let reader = LinearinterpolFastFieldReader::open_from_bytes(&out).unwrap();
-        for (doc, val) in data.iter().enumerate() {
-            assert_eq!(reader.get_u64(doc as u64), *val);
-        }
-        (reader.rel_max_value, reader.offset)
-    }
-
-    #[test]
-    fn linear_interpol_fast_field_test_simple() {
-        let data = (10..=20_u64).collect::<Vec<_>>();
-
-        let (rel_max_value, offset) = create_and_validate(&data);
-
-        assert_eq!(offset, 0);
-        assert_eq!(rel_max_value, 0);
-    }
-
-    #[test]
-    fn linear_interpol_fast_field_test_with_offset() {
-        //let data = vec![5, 50, 95, 96, 97, 98, 99, 100];
-        let mut data = vec![5, 6, 7, 8, 9, 10, 99, 100];
-        create_and_validate(&data);
-
-        data.reverse();
-        create_and_validate(&data);
-    }
-    #[test]
-    fn linear_interpol_fast_field_test_no_structure() {
-        let mut data = vec![5, 50, 3, 13, 1, 1000, 35];
-        create_and_validate(&data);
-
-        data.reverse();
-        create_and_validate(&data);
-    }
-    #[test]
-    fn linear_interpol_fast_field_rand() {
-        for i in 0..50000 {
-            let mut data = (0..1 + rand::random::<u8>() as usize)
-                .map(|num| rand::random::<i64>() as u64 / 2 as u64)
-                .collect::<Vec<_>>();
-            create_and_validate(&data);
-
-            data.reverse();
-            create_and_validate(&data);
-        }
-    }
-}
diff --git a/fastfield_codecs/src/linearinterpol/serialize.rs b/fastfield_codecs/src/linearinterpol/serialize.rs
deleted file mode 100644
index 0c99bfde0..000000000
--- a/fastfield_codecs/src/linearinterpol/serialize.rs
+++ /dev/null
@@ -1,87 +0,0 @@
-use crate::FastFieldDataAccess;
-use crate::FastFieldSerializerEstimate;
-use crate::FastFieldStats;
-use common::BinarySerializable;
-use std::io::{self, Write};
-use tantivy_bitpacker::compute_num_bits;
-use tantivy_bitpacker::BitPacker;
-
-/// Fastfield serializer, which tries to guess values by linear interpolation
-/// and stores the difference.
-pub struct LinearInterpolFastFieldSerializer {}
-
-// TODO not suitable if max is larger than i64::MAX / 2
-
-impl LinearInterpolFastFieldSerializer {
-    /// Creates a new fast field serializer.
-    pub fn create(
-        write: &mut impl Write,
-        fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-        data_iter: impl Iterator<Item = u64>,
-        data_iter1: impl Iterator<Item = u64>,
-        data_iter2: impl Iterator<Item = u64>,
-    ) -> io::Result<()> {
-        assert!(stats.min_value <= stats.max_value);
-
-        //let first_val = stats.min_value;
-        //let last_val = stats.max_value;
-        let first_val = fastfield_accessor.get(0);
-        let last_val = fastfield_accessor.get(stats.num_vals as u32 - 1);
-        let slope = (last_val as f64 - first_val as f64) / (stats.num_vals as u64 - 1) as f64;
-        // offset to ensure all values are positive
-        let offset = data_iter1
-            .enumerate()
-            .map(|(pos, val)| {
-                let calculated_value = first_val + (pos as f64 * slope) as u64;
-                val as i64 - calculated_value as i64
-            })
-            .min()
-            .unwrap()
-            .abs() as u64;
-
-        //calc new max
-        let rel_max = data_iter2
-            .enumerate()
-            .map(|(pos, val)| {
-                let calculated_value = first_val + (pos as f64 * slope) as u64;
-                (val + offset) - calculated_value
-            })
-            .max()
-            .unwrap();
-
-        let amplitude = rel_max;
-        amplitude.serialize(write)?;
-        offset.serialize(write)?;
-        first_val.serialize(write)?;
-        last_val.serialize(write)?;
-        stats.num_vals.serialize(write)?;
-        let num_bits = compute_num_bits(amplitude);
-        let mut bit_packer = BitPacker::new();
-        for (pos, val) in data_iter.enumerate() {
-            let calculated_value = first_val + (pos as f64 * slope) as u64;
-            let diff = (val + offset) - calculated_value;
-            bit_packer.write(diff, num_bits, write)?;
-        }
-        bit_packer.close(write)?;
-
-        Ok(())
-    }
-}
-
-impl FastFieldSerializerEstimate for LinearInterpolFastFieldSerializer {
-    fn estimate(
-        _fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-    ) -> (f32, &'static str) {
-        let amplitude = stats.max_value - stats.min_value;
-        let num_bits = compute_num_bits(amplitude);
-        let num_bits_uncompressed = 64;
-        let ratio = num_bits as f32 / num_bits_uncompressed as f32;
-        let name = Self::codec_id().0;
-        (ratio, name)
-    }
-    fn codec_id() -> (&'static str, u8) {
-        ("LinearInterpol", 2)
-    }
-}
diff --git a/src/directory/owned_bytes.rs b/src/directory/owned_bytes.rs
index 1983d41c8..d8f493416 100644
--- a/src/directory/owned_bytes.rs
+++ b/src/directory/owned_bytes.rs
@@ -56,12 +56,6 @@ impl OwnedBytes {
         self.data
     }
 
-    /// Returns the underlying slice of data.
-    /// `Deref` and `AsRef` are also available.
-    #[inline]
-    pub fn into_slice(self) -> &'static [u8] {
-        self.data
-    }
     /// Returns the len of the slice.
     #[inline]
     pub fn len(&self) -> usize {
diff --git a/src/fastfield/reader.rs b/src/fastfield/reader.rs
index 5f36a1d4d..3e86198ac 100644
--- a/src/fastfield/reader.rs
+++ b/src/fastfield/reader.rs
@@ -107,7 +107,8 @@ impl<Item: FastValue> FastFieldReader<Item> for DynamicFastFieldReader<Item> {
 /// fast field is required.
 #[derive(Clone)]
 pub struct BitpackedFastFieldReader<Item: FastValue> {
-    reader: BitpackedReader<'static>,
+    reader: BitpackedReader,
+    bytes: OwnedBytes,
     _phantom: PhantomData<Item>,
 }
 
@@ -118,16 +119,17 @@ impl<Item: FastValue> BitpackedFastFieldReader<Item> {
         let _id = u8::deserialize(&mut bytes)?;
         Self::open_from_bytes(bytes)
     }
-    /// Opens a fast field given a file.
+    /// Opens a fast field given the bytes.
     pub fn open_from_bytes(bytes: OwnedBytes) -> crate::Result<Self> {
-        let reader = BitpackedReader::open_from_bytes(bytes.into_slice())?;
+        let reader = BitpackedReader::open_from_bytes(bytes.as_slice())?;
         Ok(BitpackedFastFieldReader {
             reader,
+            bytes,
             _phantom: PhantomData,
         })
     }
     pub(crate) fn get_u64(&self, doc: u64) -> Item {
-        Item::from_u64(self.reader.get_u64(doc))
+        Item::from_u64(self.reader.get_u64(doc, self.bytes.as_slice()))
     }
 
     /// Internally `multivalued` also use SingleValue Fast fields.
diff --git a/src/fastfield/serializer/bitpacked.rs b/src/fastfield/serializer/bitpacked.rs
deleted file mode 100644
index 8dc6e9c4f..000000000
--- a/src/fastfield/serializer/bitpacked.rs
+++ /dev/null
@@ -1,97 +0,0 @@
-use super::FastFieldDataAccess;
-use super::FastFieldSerializer;
-use super::FastFieldSerializerEstimate;
-use super::FastFieldStats;
-use crate::common::BinarySerializable;
-use std::io::{self, Write};
-use tantivy_bitpacker::compute_num_bits;
-use tantivy_bitpacker::BitPacker;
-
-pub struct BitpackedFastFieldSerializer<'a, W: 'a + Write> {
-    bit_packer: BitPacker,
-    write: &'a mut W,
-    min_value: u64,
-    num_bits: u8,
-}
-
-impl<'a, W: Write> BitpackedFastFieldSerializer<'a, W> {
-    /// Creates a new fast field serializer.
-    ///
-    /// The serializer in fact encode the values by bitpacking
-    /// `(val - min_value)`.
-    ///
-    /// It requires a `min_value` and a `max_value` to compute
-    /// compute the minimum number of bits required to encode
-    /// values.
-    pub(crate) fn open(
-        write: &'a mut W,
-        min_value: u64,
-        max_value: u64,
-    ) -> io::Result<BitpackedFastFieldSerializer<'a, W>> {
-        assert!(min_value <= max_value);
-        min_value.serialize(write)?;
-        let amplitude = max_value - min_value;
-        amplitude.serialize(write)?;
-        let num_bits = compute_num_bits(amplitude);
-        let bit_packer = BitPacker::new();
-        Ok(BitpackedFastFieldSerializer {
-            bit_packer,
-            write,
-            min_value,
-            num_bits,
-        })
-    }
-    /// Creates a new fast field serializer.
-    ///
-    /// The serializer in fact encode the values by bitpacking
-    /// `(val - min_value)`.
-    ///
-    /// It requires a `min_value` and a `max_value` to compute
-    /// compute the minimum number of bits required to encode
-    /// values.
-    pub(crate) fn create(
-        write: &'a mut W,
-        fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-        data_iter: impl Iterator<Item = u64>,
-    ) -> io::Result<()> {
-        let mut serializer = Self::open(write, stats.min_value, stats.max_value)?;
-
-        for val in data_iter {
-            serializer.add_val(val)?;
-        }
-        serializer.close_field()?;
-
-        Ok(())
-    }
-}
-
-impl<'a, W: 'a + Write> FastFieldSerializer for BitpackedFastFieldSerializer<'a, W> {
-    /// Pushes a new value to the currently open u64 fast field.
-    fn add_val(&mut self, val: u64) -> io::Result<()> {
-        let val_to_write: u64 = val - self.min_value;
-        self.bit_packer
-            .write(val_to_write, self.num_bits, &mut self.write)?;
-        Ok(())
-    }
-    fn close_field(mut self) -> io::Result<()> {
-        self.bit_packer.close(&mut self.write)
-    }
-}
-
-impl<'a, W: 'a + Write> FastFieldSerializerEstimate for BitpackedFastFieldSerializer<'a, W> {
-    fn estimate(
-        _fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-    ) -> (f32, &'static str) {
-        let amplitude = stats.max_value - stats.min_value;
-        let num_bits = compute_num_bits(amplitude);
-        let num_bits_uncompressed = 64;
-        let ratio = num_bits as f32 / num_bits_uncompressed as f32;
-        let name = Self::codec_id().0;
-        (ratio, name)
-    }
-    fn codec_id() -> (&'static str, u8) {
-        ("Bitpacked", 1)
-    }
-}
diff --git a/src/fastfield/serializer/linearinterpol.rs b/src/fastfield/serializer/linearinterpol.rs
deleted file mode 100644
index 888a33146..000000000
--- a/src/fastfield/serializer/linearinterpol.rs
+++ /dev/null
@@ -1,78 +0,0 @@
-use super::FastFieldDataAccess;
-use super::FastFieldSerializerEstimate;
-use super::FastFieldStats;
-use crate::common::BinarySerializable;
-use std::io::{self, Write};
-use tantivy_bitpacker::compute_num_bits;
-use tantivy_bitpacker::BitPacker;
-
-/// Fastfield serializer, which tries to guess values by linear interpolation
-/// and stores the difference.
-pub struct LinearInterpolFastFieldSerializer {}
-
-impl LinearInterpolFastFieldSerializer {
-    /// Creates a new fast field serializer.
-    pub(crate) fn create(
-        write: &mut impl Write,
-        _fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-        data_iter: impl Iterator<Item = u64>,
-        data_iter1: impl Iterator<Item = u64>,
-        data_iter2: impl Iterator<Item = u64>,
-    ) -> io::Result<()> {
-        assert!(stats.min_value <= stats.max_value);
-
-        let step = (stats.max_value - stats.min_value) as f64 / (stats.num_vals as u64 - 1) as f64;
-        // offset to ensure all values are positive
-        let offset = data_iter1
-            .enumerate()
-            .map(|(pos, val)| {
-                let calculated_value = stats.min_value + (pos as f64 * step) as u64;
-                val as i64 - calculated_value as i64
-            })
-            .min()
-            .unwrap()
-            .abs() as u64;
-
-        //calc new max
-        let rel_max = data_iter2
-            .enumerate()
-            .map(|(pos, val)| {
-                let calculated_value = stats.min_value + (pos as f64 * step) as u64;
-                (val + offset) - calculated_value
-            })
-            .max()
-            .unwrap();
-
-        stats.min_value.serialize(write)?;
-        let amplitude = rel_max;
-        amplitude.serialize(write)?;
-        offset.serialize(write)?;
-        stats.min_value.serialize(write)?;
-        let num_bits = compute_num_bits(amplitude);
-        let mut bit_packer = BitPacker::new();
-        for val in data_iter {
-            bit_packer.write(val, num_bits, write)?;
-        }
-        bit_packer.close(write)?;
-
-        Ok(())
-    }
-}
-
-impl FastFieldSerializerEstimate for LinearInterpolFastFieldSerializer {
-    fn estimate(
-        _fastfield_accessor: &impl FastFieldDataAccess,
-        stats: FastFieldStats,
-    ) -> (f32, &'static str) {
-        let amplitude = stats.max_value - stats.min_value;
-        let num_bits = compute_num_bits(amplitude);
-        let num_bits_uncompressed = 64;
-        let ratio = num_bits as f32 / num_bits_uncompressed as f32;
-        let name = Self::codec_id().0;
-        (ratio, name)
-    }
-    fn codec_id() -> (&'static str, u8) {
-        ("LinearInterpol", 2)
-    }
-}
diff --git a/src/fastfield/serializer/mod.rs b/src/fastfield/serializer/mod.rs
index 14050a217..26669d6e3 100644
--- a/src/fastfield/serializer/mod.rs
+++ b/src/fastfield/serializer/mod.rs
@@ -1,12 +1,9 @@
-mod bitpacked;
-mod linearinterpol;
-
 use crate::common::BinarySerializable;
 use crate::common::CompositeWrite;
 use crate::common::CountingWriter;
 use crate::directory::WritePtr;
 use crate::schema::Field;
-use crate::DocId;
+use fastfield_codecs::CodecId;
 //pub use bitpacked::BitpackedFastFieldSerializer;
 pub use fastfield_codecs::bitpacked::BitpackedFastFieldSerializer;
 pub use fastfield_codecs::FastFieldDataAccess;
@@ -57,13 +54,14 @@ impl CompositeFastFieldSerializer {
     ) -> io::Result<()> {
         let field_write = self.composite_write.for_field_with_idx(field, 0);
 
-        let (_ratio, (name, id)) = (
+        let (_ratio, name, id) = (
             BitpackedFastFieldSerializer::<Vec<u8>>::estimate(&fastfield_accessor, stats.clone()),
-            BitpackedFastFieldSerializer::<Vec<u8>>::codec_id(),
+            BitpackedFastFieldSerializer::<Vec<u8>>::NAME,
+            BitpackedFastFieldSerializer::<Vec<u8>>::ID,
         );
 
         id.serialize(field_write)?;
-        if name == BitpackedFastFieldSerializer::<Vec<u8>>::codec_id().0 {
+        if name == BitpackedFastFieldSerializer::<Vec<u8>>::NAME {
             BitpackedFastFieldSerializer::create(
                 field_write,
                 &fastfield_accessor,
@@ -97,7 +95,7 @@ impl CompositeFastFieldSerializer {
     ) -> io::Result<BitpackedFastFieldSerializer<'_, CountingWriter<WritePtr>>> {
         let field_write = self.composite_write.for_field_with_idx(field, idx);
         // Prepend codec id to field data for compatibility with DynamicFastFieldReader.
-        let (_name, id) = BitpackedFastFieldSerializer::<Vec<u8>>::codec_id();
+        let id = BitpackedFastFieldSerializer::<Vec<u8>>::ID;
         id.serialize(field_write)?;
         BitpackedFastFieldSerializer::open(field_write, min_value, max_value)
     }