remove duplication

src/lib/provable/gadgets/sha256.ts

@@ -8,7 +8,6 @@ import { Bytes } from '../wrapped-classes.js';
 import { chunk } from '../../util/arrays.js';
 import { TupleN } from '../../util/types.js';
 import { divMod32 } from './arithmetic.js';
-import { bytesToWord, wordToBytes } from './bit-slices.js';
 import { bitSlice } from './common.js';
 import { rangeCheck16 } from './range-check.js';
 
@@ -70,11 +69,7 @@ function padding(data: FlexibleBytes): UInt32[][] {
   for (let i = 0; i < paddedMessage.length; i += 4) {
     // chunk 4 bytes into one UInt32, as expected by SHA256
     // bytesToWord expects little endian, so we reverse the bytes
-    chunks.push(
-      UInt32.Unsafe.fromField(
-        bytesToWord(paddedMessage.slice(i, i + 4).reverse())
-      )
-    );
+    chunks.push(UInt32.fromBytesBE(paddedMessage.slice(i, i + 4)));
   }
 
   // split message into 16 element sized message blocks
@@ -97,8 +92,7 @@ const SHA256 = {
     }
 
     // the working variables H[i] are 32bit, however we want to decompose them into bytes to be more compatible
-    // wordToBytes expects little endian, so we reverse the bytes
-    return Bytes.from(H.map((x) => wordToBytes(x.value, 4).reverse()).flat());
+    return Bytes.from(H.map((x) => x.toBytesBE()).flat());
   },
   compression: sha256Compression,
   createMessageSchedule,

src/lib/provable/int.ts

@@ -19,6 +19,7 @@ import {
 } from './gadgets/comparison.js';
 import { assert } from '../util/assert.js';
 import { TupleN } from '../util/types.js';
+import { bytesToWord, wordToBytes } from './gadgets/bit-slices.js';
 
 // external API
 export { UInt8, UInt32, UInt64, Int64, Sign };
@@ -961,35 +962,23 @@ class UInt32 extends CircuitValue {
   /**
    * Split a UInt32 into 4 UInt8s, in little-endian order.
    */
-  toBytes(): TupleN<UInt8, 4> {
-    // witness the bytes
-    let bytes = Provable.witness(Provable.Array(UInt8, 4), () => {
-      let x = this.value.toBigInt();
-      return [0, 1, 2, 3].map((i) => UInt8.from((x >> BigInt(8 * i)) & 0xffn));
-    });
-    // prove that bytes are correct
-    UInt32.fromBytes(bytes).assertEquals(this);
-    return TupleN.fromArray(4, bytes);
+  toBytes() {
+    return TupleN.fromArray(4, wordToBytes(this.value, 4));
   }
 
   /**
    * Split a UInt32 into 4 UInt8s, in big-endian order.
    */
-  toBytesBE(): TupleN<UInt8, 4> {
-    return TupleN.fromArray(4, this.toBytes().reverse());
+  toBytesBE() {
+    return TupleN.fromArray(4, wordToBytes(this.value, 4).reverse());
   }
 
   /**
    * Combine 4 UInt8s into a UInt32, in little-endian order.
    */
   static fromBytes(bytes: UInt8[]): UInt32 {
     assert(bytes.length === 4, '4 bytes needed to create a uint32');
-
-    let word = Field(0);
-    bytes.forEach(({ value }, i) => {
-      word = word.add(value.mul(1n << BigInt(8 * i)));
-    });
-    return UInt32.Unsafe.fromField(word);
+    return UInt32.Unsafe.fromField(bytesToWord(bytes));
   }
 
   /**