From 3b3e26c4b8b2a4e67645c2038dae93d50f280564 Mon Sep 17 00:00:00 2001
From: Pascal Seitz <pascal.seitz@gmail.com>
Date: Tue, 8 Jun 2021 13:02:42 +0200
Subject: [PATCH] use f64 precision for slope calculation

---
 fastfield_codecs/src/linearinterpol.rs |  6 ++++--
 src/common/mod.rs                      |  4 ----
 src/fastfield/reader.rs                | 11 ++++-------
 src/fastfield/serializer/mod.rs        |  1 -
 4 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/fastfield_codecs/src/linearinterpol.rs b/fastfield_codecs/src/linearinterpol.rs
index b3aea0de3..1bf7c8b9c 100644
--- a/fastfield_codecs/src/linearinterpol.rs
+++ b/fastfield_codecs/src/linearinterpol.rs
@@ -152,7 +152,9 @@ impl LinearInterpolFastFieldSerializer {
     }
 }
 fn get_slope(first_val: u64, last_val: u64, num_vals: u64) -> f32 {
-    (last_val as f32 - first_val as f32) / (num_vals as u64 - 1) as f32
+    //  We calculate the slope with f64 high precision and use the result in lower precision f32
+    //  This is done in order to handle estimation for very large values like i64::MAX
+    ((last_val as f64 - first_val as f64) / (num_vals as u64 - 1) as f64) as f32
 }
 
 fn get_calculated_value(first_val: u64, pos: u64, slope: f32) -> u64 {
@@ -163,7 +165,7 @@ impl FastFieldSerializerEstimate for LinearInterpolFastFieldSerializer {
     /// where the local maxima are for the deviation of the calculated value and
     /// the offset is also unknown.
     fn estimate(fastfield_accessor: &impl FastFieldDataAccess, stats: FastFieldStats) -> f32 {
-        if stats.max_value > i64::MAX as u64 / 2 || stats.num_vals < 3 {
+        if (stats.max_value - stats.min_value) > i64::MAX as u64 / 2 || stats.num_vals < 3 {
             return f32::MAX; //disable compressor for this case
         }
         let first_val = fastfield_accessor.get(0);
diff --git a/src/common/mod.rs b/src/common/mod.rs
index 4e574f1a0..29a4b057c 100644
--- a/src/common/mod.rs
+++ b/src/common/mod.rs
@@ -1,14 +1,11 @@
 mod bitset;
 mod composite_file;
 mod counting_writer;
-//mod serialize;
-//mod vint;
 
 pub use self::bitset::BitSet;
 pub(crate) use self::bitset::TinySet;
 pub(crate) use self::composite_file::{CompositeFile, CompositeWrite};
 pub use self::counting_writer::CountingWriter;
-//pub use self::serialize::{BinarySerializable, DeserializeFrom, FixedSize};
 pub use byteorder::LittleEndian as Endianness;
 pub use common::{
     read_u32_vint, read_u32_vint_no_advance, serialize_vint_u32, write_u32_vint, VInt,
@@ -104,7 +101,6 @@ pub fn u64_to_f64(val: u64) -> f64 {
 #[cfg(test)]
 pub(crate) mod test {
 
-    //pub use super::serialize::test::fixed_size_test;
     use super::{f64_to_u64, i64_to_u64, u64_to_f64, u64_to_i64};
     use common::{BinarySerializable, FixedSize};
     use proptest::prelude::*;
diff --git a/src/fastfield/reader.rs b/src/fastfield/reader.rs
index 1b093c9f4..8cb7ec089 100644
--- a/src/fastfield/reader.rs
+++ b/src/fastfield/reader.rs
@@ -73,24 +73,21 @@ pub enum DynamicFastFieldReader<Item: FastValue> {
 impl<Item: FastValue> DynamicFastFieldReader<Item> {
     /// Returns correct the reader wrapped in the `DynamicFastFieldReader` enum for the data.
     pub fn open(file: FileSlice) -> crate::Result<DynamicFastFieldReader<Item>> {
-        let bytes = file.read_bytes()?;
-        let (mut id_bytes, data_bytes) = bytes.split(1);
-        let id = u8::deserialize(&mut id_bytes)?;
+        let mut bytes = file.read_bytes()?;
+        let id = bytes.read_u8();
 
         let reader = match id {
             BitpackedFastFieldSerializer::<Vec<u8>>::ID => {
                 DynamicFastFieldReader::Bitpacked(FastFieldReaderCodecWrapper::<
                     Item,
                     BitpackedReader,
-                >::open_from_bytes(data_bytes)?)
+                >::open_from_bytes(bytes)?)
             }
             LinearInterpolFastFieldSerializer::ID => {
                 DynamicFastFieldReader::LinearInterpol(FastFieldReaderCodecWrapper::<
                     Item,
                     LinearinterpolFastFieldReader,
-                >::open_from_bytes(
-                    data_bytes
-                )?)
+                >::open_from_bytes(bytes)?)
             }
             _ => {
                 panic!(
diff --git a/src/fastfield/serializer/mod.rs b/src/fastfield/serializer/mod.rs
index 8d358326e..8a48199a6 100644
--- a/src/fastfield/serializer/mod.rs
+++ b/src/fastfield/serializer/mod.rs
@@ -78,7 +78,6 @@ impl CompositeFastFieldSerializer {
         }
         estimations.sort_by(|a, b| a.0.partial_cmp(&b.0).unwrap());
         let (_ratio, name, id) = estimations[0];
-        //estimations.sort_by_key(|el| el.0);
         id.serialize(field_write)?;
         match name {
             BitpackedFastFieldSerializer::<Vec<u8>>::NAME => {