perf: avoid typed-array iteration in shared SHA-256 blocks (#20346)

Co-authored-by: Orca Worker <orca-worker@localhost>

src/shared/sha256.test.ts

@@ -0,0 +1,16 @@
+import { createHash } from 'node:crypto'
+import { describe, expect, it } from 'vitest'
+import { sha256 } from './sha256'
+
+describe('shared sha256', () => {
+  it.each([0, 1, 55, 56, 63, 64, 65, 119, 120, 127, 128, 1024, 65_536])(
+    'matches Node crypto for a %i-byte offset view',
+    (length) => {
+      const backing = Uint8Array.from({ length: length + 7 }, (_, index) => index % 251)
+      const bytes = backing.subarray(7)
+      expect(Buffer.from(sha256(bytes)).toString('hex')).toBe(
+        createHash('sha256').update(bytes).digest('hex')
+      )
+    }
+  )
+})

src/shared/sha256.ts

@@ -43,7 +43,14 @@ export function sha256(message: Uint8Array): Uint8Array {
       words[index] = (words[index - 16] + s0 + words[index - 7] + s1) | 0
     }
 
-    let [a, b, c, d, e, f, g, h] = hash
+    let a = hash[0]
+    let b = hash[1]
+    let c = hash[2]
+    let d = hash[3]
+    let e = hash[4]
+    let f = hash[5]
+    let g = hash[6]
+    let h = hash[7]
     for (let index = 0; index < 64; index += 1) {
       const sigma1 = rotateRight(e, 6) ^ rotateRight(e, 11) ^ rotateRight(e, 25)
       const choice = (e & f) ^ (~e & g)