fix(ssa): Remove padding from ToRadix call with constant inputs

crates/nargo_cli/tests/execution_success/to_bytes_consistent/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "to_bytes_consistent"
+type = "bin"
+authors = [""]
+compiler_version = "0.10.3"
+
+[dependencies]

crates/nargo_cli/tests/execution_success/to_bytes_consistent/Prover.toml

@@ -0,0 +1 @@
+x = "2040124"

crates/nargo_cli/tests/execution_success/to_bytes_consistent/src/main.nr

@@ -0,0 +1,14 @@
+// This test aims to check that we have consistent behavior 
+// between a `to_be_bytes` call (which is radix decomposition under the hood) 
+// with constant inputs or with witness inputs.
+
+// x = 2040124
+fn main(x : Field) {
+    let byte_array = x.to_be_bytes(31);
+    let x_as_constant = 2040124;
+    let constant_byte_array = x_as_constant.to_be_bytes(31);
+    assert(constant_byte_array.len() == byte_array.len());
+    for i in 0..constant_byte_array.len() {
+        assert(constant_byte_array[i] == byte_array[i]);
+    }
+}

crates/noirc_evaluator/src/ssa/ir/instruction/call.rs

@@ -221,7 +221,7 @@
 
 /// Slices have a tuple structure (slice length, slice contents) to enable logic
 /// that uses dynamic slice lengths (such as with merging slices in the flattening pass).
 /// This method codegens an update to the slice length.
 ///
 /// The binary operation performed on the slice length is always an addition or subtraction of `1`.
 /// This is because the slice length holds the user length (length as displayed by a `.len()` call),
@@ -334,15 +334,6 @@
         limbs.reverse();
     }
 
-    // For legacy reasons (see #617) the to_radix interface supports 256 bits even though
-    // FieldElement::max_num_bits() is only 254 bits. Any limbs beyond the specified count
-    // become zero padding.
-    let max_decomposable_bits: u32 = 256;
-    let limb_count_with_padding = max_decomposable_bits / bit_size;
-    while limbs.len() < limb_count_with_padding as usize {
-        limbs.push(FieldElement::zero());
-    }
-
     make_constant_array(dfg, limbs, Type::unsigned(bit_size))
 }
 

crates/noirc_evaluator/src/ssa/ssa_builder/mod.rs

@@ -385,7 +385,7 @@ mod tests {
 
     #[test]
     fn insert_constant_call() {
-        // `bits` should be an array of constants [1, 1, 1, 0...]:
+        // `bits` should be an array of constants [1, 1, 1, 0...] of length 8:
         // let x = 7;
         // let bits = x.to_le_bits(8);
         let func_id = Id::test_new(0);
@@ -404,7 +404,7 @@ mod tests {
             Value::NumericConstant { constant, .. } => *constant,
             _ => panic!(),
         };
-        assert_eq!(slice_len, FieldElement::from(256u128));
+        assert_eq!(slice_len, FieldElement::from(8_u128));
 
         let slice = match &builder.current_function.dfg[call_results[1]] {
             Value::Array { array, .. } => array,