circuit: use SubArraySelector in ByteSubArrayToInts

zkemail · Apr 1, 2024 · b1d2052 · b1d2052
1 parent 66bf305
commit b1d2052
Show file tree

Hide file tree

Showing 2 changed files with 17 additions and 20 deletions.
diff --git a/packages/circuits/utils/bytes.circom b/packages/circuits/utils/bytes.circom
@@ -62,9 +62,12 @@ template BytesToInts(maxBytes) {
 
 /// @title ByteSubArrayToInts
 /// @notice Select sub array from a byte array and pack to a 31-byte integer array
-/// @notice This is not used in the main circuits
-/// @param maxBytes: the maximum number of bytes in the input array
+/// @notice This is not used in ZK-Email circuits anywhere
+/// @param maxArrayLen: the maximum number of elements in the input array
+/// @param maxSubArrayLen: the maximum number of elements in the sub array
 /// @input in: the input byte array
+/// @input startIndex: the start index of the sub array
+/// @input length: the length of the sub array
 /// @output out: the output integer array
 template ByteSubArrayToInts(maxArrayLen, maxSubArrayLen) {
     assert(maxSubArrayLen < maxArrayLen);
@@ -76,24 +79,15 @@ template ByteSubArrayToInts(maxArrayLen, maxSubArrayLen) {
 
     signal output out[chunkLength];
 
-    assert(length < maxSubArrayLen);
+    assert(length <= maxSubArrayLen);
 
-    component shifter = ArrayShiftLeft(maxArrayLen, maxSubArrayLen);
-    shifter.in <== in;
-    shifter.shift <== startIndex;
+    component subarraySelector = SubArraySelector(maxArrayLen, maxSubArrayLen);
+    subarraySelector.in <== in;
+    subarraySelector.startIndex <== startIndex;
+    subarraySelector.length <== length;
 
     component packer = BytesToInts(maxSubArrayLen);
-
-    // Set value after length to zero
-    component gts[maxSubArrayLen];
-    for (var i = 0; i < maxSubArrayLen; i++) {
-        gts[i] = GreaterThan(log2Ceil(maxSubArrayLen));
-        gts[i].in[0] <== length;
-        gts[i].in[1] <== i;
-
-        packer.in[i] <== gts[i].out * shifter.out[i];
-    }
-
+    packer.in <== subarraySelector.out;
 
     out <== packer.out;
 }

diff --git a/packages/circuits/utils/extract.circom b/packages/circuits/utils/extract.circom
@@ -6,19 +6,20 @@ include "./bytes.circom";
 
 /// @title ExtractRegexReveal
 /// @notice Extracts reveal part from a regex match
+/// @notice Verifies data before and after (maxRevealLen) reveal part is zero
 /// @param maxArrayLen Maximum length of the input array
 /// @param maxRevealLen Maximum length of the reveal part
 /// @input in Input array
 /// @input startIndex Index of the start of the reveal part
 /// @output out Revealed data array
 template ExtractRegexReveal(maxArrayLen, maxRevealLen) {
-    var bitLength = log2Ceil(maxArrayLen);
-
     signal input in[maxArrayLen];
     signal input startIndex;
 
     signal output out[maxRevealLen];
-
+
+    var bitLength = log2Ceil(maxArrayLen);
+
     signal isStartIndex[maxArrayLen];
     signal isZero[maxArrayLen];
     signal isPreviousZero[maxArrayLen];
@@ -68,6 +69,8 @@ template PackRegexReveal(maxArrayLen, maxRevealLen) {
     extractor.in <== in;
     extractor.startIndex <== startIndex;
 
+    // Items after reveal part and before maxRevealLen are already asserted to zero
+    // So we can safely pack without an additional `length` input
     component packer = BytesToInts(maxRevealLen);
     packer.in <== extractor.out;
     out <== packer.out;