Remove redundant range check in rotation gadget

src/examples/primitive_constraint_system.ts

@@ -66,6 +66,7 @@ const GroupMock = {
 const BitwiseMock = {
   rot() {
     let a = Provable.witness(Field, () => new Field(12));
+    Gadgets.rangeCheck64(a); // `rotate()` doesn't do this
     Gadgets.rotate(a, 2, 'left');
     Gadgets.rotate(a, 2, 'right');
     Gadgets.rotate(a, 4, 'left');

src/examples/regression_test.json

@@ -169,8 +169,8 @@
     "digest": "Bitwise Primitive",
     "methods": {
       "rot": {
-        "rows": 13,
-        "digest": "2c0dadbba96fd7ddb9adb7d643425ce3"
+        "rows": 10,
+        "digest": "c38703de755b10edf77bf24269089274"
       },
       "xor": {
         "rows": 15,

src/lib/gadgets/bitwise.ts

@@ -194,7 +194,9 @@ function rot(
   );
   // Compute next row
   Gates.rangeCheck64(shifted);
-  // Compute following row
-  Gates.rangeCheck64(excess);
+  // note: range-checking `shifted` and `field` is enough.
+  // * excess < 2^rot follows from the bound check and the rotation equation in the gate
+  // * rotated < 2^64 follows from rotated = excess + shifted (because shifted has to be a multiple of 2^rot)
+  // for a proof, see https://github.com/o1-labs/o1js/pull/1201
   return [rotated, excess, shifted];
 }

src/lib/gadgets/bitwise.unit-test.ts

@@ -1,7 +1,7 @@
 import { ZkProgram } from '../proof_system.js';
 import {
   Spec,
-  equivalent,
+  equivalentProvable as equivalent,
   equivalentAsync,
   field,
   fieldWithRng,