fix(old ssa): fix to_be_bits (#1765)

* fix to_le_bits in original ssa

* add test

crates/nargo_cli/tests/test_data/to_bits/Nargo.toml

@@ -0,0 +1,5 @@
+[package]
+authors = [""]
+compiler_version = "0.7.0"
+
+[dependencies]

crates/nargo_cli/tests/test_data/to_bits/src/main.nr

@@ -0,0 +1,24 @@
+use dep::std;
+
+fn main() {
+    let field = 1000;
+    let be_bits = field.to_be_bits(16);
+    let le_bits = field.to_le_bits(16);
+
+    for i in 0..16 {
+        let x = be_bits[i];
+        let y = le_bits[15-i];
+        assert(x == y);
+    }
+
+    let x = 3;
+    let be_bits_x = x.to_be_bits(4);
+    let le_bits_x = x.to_le_bits(4);
+
+    for i in 0..4 {
+        let be_bit = be_bits_x[i];
+        let le_bit = le_bits_x[3-i];
+        assert(be_bit == le_bit);
+    }
+
+}

crates/noirc_evaluator/src/ssa/optimizations.rs

@@ -79,11 +79,15 @@ fn evaluate_intrinsic(
     block_id: BlockId,
 ) -> Result<Vec<NodeId>, RuntimeErrorKind> {
     match op {
-        builtin::Opcode::ToBits(_) => {
+        builtin::Opcode::ToBits(endian) => {
             let bit_count = args[1].to_u128() as u32;
             let mut result = Vec::new();
             let mut bits = args[0].bits();
             bits.reverse();
+            bits.resize(bit_count as usize, false);
+            if endian == builtin::Endian::Big {
+                bits.reverse();
+            }
 
             if let ObjectType::ArrayPointer(a) = res_type {
                 for i in 0..bit_count {