Add Bit struct to stdlib

examples/fixture/asm/kimchi/generic_builtin_bits.asm

@@ -11,9 +11,6 @@ DoubleGeneric<1,0,-1,0,1>
 DoubleGeneric<1,-1>
 DoubleGeneric<0,0,-1,1>
 DoubleGeneric<1>
-DoubleGeneric<1,0,-1>
-DoubleGeneric<1,1>
-DoubleGeneric<1,0,-1,0,1>
 DoubleGeneric<1,1>
 DoubleGeneric<1,1,-1>
 DoubleGeneric<0,0,-1,1>
@@ -22,9 +19,6 @@ DoubleGeneric<1,0,-1,0,1>
 DoubleGeneric<1,-1>
 DoubleGeneric<0,0,-1,1>
 DoubleGeneric<1>
-DoubleGeneric<1,0,-1>
-DoubleGeneric<1,1>
-DoubleGeneric<1,0,-1,0,1>
 DoubleGeneric<1,1>
 DoubleGeneric<1,1,-1>
 DoubleGeneric<0,0,-1,1>
@@ -36,9 +30,6 @@ DoubleGeneric<1>
 DoubleGeneric<1,0,-1>
 DoubleGeneric<1,1>
 DoubleGeneric<1,0,-1,0,1>
-DoubleGeneric<1,0,-1>
-DoubleGeneric<1,1>
-DoubleGeneric<1,0,-1,0,1>
 DoubleGeneric<2,0,-1>
 DoubleGeneric<1,1>
 DoubleGeneric<1,0,-1,0,1>
@@ -68,52 +59,46 @@ DoubleGeneric<1,0,-1,0,1>
 DoubleGeneric<1,1,-1>
 DoubleGeneric<1,-1>
 DoubleGeneric<1,0,0,0,-2>
-(0,0) -> (46,1) -> (65,1) -> (66,0)
-(1,0) -> (3,0) -> (14,0) -> (25,0)
+(0,0) -> (37,1) -> (56,1) -> (57,0)
+(1,0) -> (3,0) -> (11,0) -> (19,0)
 (2,1) -> (3,1)
 (3,2) -> (4,1) -> (8,1)
 (4,2) -> (7,0)
-(5,0) -> (8,0) -> (10,0) -> (11,0)
+(5,0) -> (8,0) -> (26,0) -> (27,0) -> (38,0) -> (45,0) -> (46,0)
 (5,1) -> (6,0)
 (6,2) -> (7,1)
 (8,2) -> (9,0)
-(10,2) -> (35,0) -> (36,0) -> (47,0) -> (54,0) -> (55,0)
-(11,1) -> (12,0)
-(13,1) -> (14,1)
-(14,2) -> (15,1) -> (19,1)
-(15,2) -> (18,0)
-(16,0) -> (19,0) -> (21,0) -> (22,0)
-(16,1) -> (17,0)
-(17,2) -> (18,1)
-(19,2) -> (20,0)
-(21,2) -> (38,0) -> (39,0) -> (50,0) -> (57,0) -> (58,0)
-(22,1) -> (23,0)
-(24,1) -> (25,1)
-(25,2) -> (26,1) -> (30,1)
-(26,2) -> (29,0)
-(27,0) -> (30,0) -> (32,0) -> (33,0)
+(10,1) -> (11,1)
+(11,2) -> (12,1) -> (16,1)
+(12,2) -> (15,0)
+(13,0) -> (16,0) -> (29,0) -> (30,0) -> (41,0) -> (48,0) -> (49,0)
+(13,1) -> (14,0)
+(14,2) -> (15,1)
+(16,2) -> (17,0)
+(18,1) -> (19,1)
+(19,2) -> (20,1) -> (24,1)
+(20,2) -> (23,0)
+(21,0) -> (24,0) -> (33,0) -> (34,0) -> (42,0) -> (52,0) -> (53,0)
+(21,1) -> (22,0)
+(22,2) -> (23,1)
+(24,2) -> (25,0)
+(26,2) -> (32,0)
 (27,1) -> (28,0)
-(28,2) -> (29,1)
-(30,2) -> (31,0)
-(32,2) -> (42,0) -> (43,0) -> (51,0) -> (61,0) -> (62,0)
-(33,1) -> (34,0)
-(35,2) -> (41,0)
-(36,1) -> (37,0)
-(38,2) -> (41,1)
-(39,1) -> (40,0)
-(41,2) -> (45,0)
-(42,2) -> (45,1)
-(43,1) -> (44,0)
-(45,2) -> (46,0)
-(47,1) -> (48,0)
-(48,2) -> (49,0)
-(51,1) -> (52,0)
-(52,2) -> (53,0)
-(54,2) -> (60,0)
-(55,1) -> (56,0)
-(57,2) -> (60,1)
-(58,1) -> (59,0)
-(60,2) -> (64,0)
-(61,2) -> (64,1)
-(62,1) -> (63,0)
-(64,2) -> (65,0)
+(29,2) -> (32,1)
+(30,1) -> (31,0)
+(32,2) -> (36,0)
+(33,2) -> (36,1)
+(34,1) -> (35,0)
+(36,2) -> (37,0)
+(38,1) -> (39,0)
+(39,2) -> (40,0)
+(42,1) -> (43,0)
+(43,2) -> (44,0)
+(45,2) -> (51,0)
+(46,1) -> (47,0)
+(48,2) -> (51,1)
+(49,1) -> (50,0)
+(51,2) -> (55,0)
+(52,2) -> (55,1)
+(53,1) -> (54,0)
+(55,2) -> (56,0)

src/stdlib/native/bits/lib.no

@@ -10,6 +10,37 @@
 /// 
 hint fn nth_bit(value: Field, const nth: Field) -> Field;
 
+/// A `Field` value representing a bit.
+/// Use `Bit.new` to create with a range-checked value.
+struct Bit {
+    inner: Field,
+}
+
+/// Creates a `Bit` without any range check on `val`.
+fn Bit.new_unchecked(val: Field) -> Bit {
+    return Bit {
+        inner: val
+    };
+}
+
+/// Creates a `Bit` with a range check on `val` so that it must be `0` or `1`.
+///
+/// # Panics
+/// - `val` is neither `0` nor `1`.
+fn Bit.new(val: Field) -> Bit {
+    assert_eq(val * (val - 1), 0);
+
+    return Bit.new_unchecked(val);
+}
+
+/// Converts to a boolean.
+///
+/// # Returns
+/// - `Bool`: `true` if value is `1` and `false` otherwise.
+fn Bit.to_bool(self) -> Bool {
+    return self.inner == 1;
+}
+
 /// Converts an array of boolean values (`bits`) into a `Field` value.
 ///
 /// # Parameters
@@ -56,21 +87,16 @@ fn from_bits(bits: [Bool; LEN]) -> Field {
 /// - The function asserts that `from_bits(bits)` equals `value`, ensuring the conversion is correct.
 fn to_bits(const LEN: Field, value: Field) -> [Bool; LEN] {
     let mut bits = [false; LEN];
-    let mut lc1 = 0;
-    let mut e2 = 1;
-
-    // TODO: ITE should allow literals.
-    let true_val = true;
-    let false_val = false;
 
     for index in 0..LEN {
         let bit_num = unsafe nth_bit(value, index);
 
-        // constraint the bit values to booleans
-        bits[index] = if bit_num == 1 { true_val } else { false_val };
+        // constrain the bit values to booleans
+        let bit = Bit.new_unchecked(bit_num);
+        bits[index] = bit.to_bool();
     }
 
-    // constraint the accumulative contributions of bits to be equal to the value
+    // constrain the accumulative contributions of bits to be equal to the value
     assert_eq(from_bits(bits), value);
 
     return bits;

src/tests/stdlib/bits/bit_checked.no

@@ -0,0 +1,7 @@
+use std::bits;
+
+fn main(pub val: Field) -> Bool {
+    let bit = bits::Bit.new(val);
+
+    return bit.to_bool();
+}

src/tests/stdlib/bits/bit_unchecked.no

@@ -0,0 +1,7 @@
+use std::bits;
+
+fn main(pub val: Field) -> Bool {
+    let bit = bits::Bit.new_unchecked(val);
+
+    return bit.to_bool();
+}

src/tests/stdlib/bits/mod.rs

@@ -0,0 +1,53 @@
+use crate::error::{self, ErrorKind};
+
+use super::test_stdlib;
+use error::Result;
+use rstest::rstest;
+
+#[rstest]
+#[case(r#"{"val": "0"}"#, vec!["0"])]
+#[case(r#"{"val": "1"}"#, vec!["1"])]
+fn test_bit_checked(#[case] public_inputs: &str, #[case] expected_output: Vec<&str>) -> Result<()> {
+    test_stdlib(
+        "bits/bit_checked.no",
+        None,
+        public_inputs,
+        r#"{}"#,
+        expected_output,
+    )?;
+
+    Ok(())
+}
+
+#[test]
+fn test_bit_checked_witness_failure() -> Result<()> {
+    let public_inputs = r#"{"val": "2"}"#; // should break range check
+
+    let err = test_stdlib("bits/bit_checked.no", None, public_inputs, r#"{}"#, vec![])
+        .err()
+        .expect("expected witness error");
+
+    assert!(matches!(err.kind, ErrorKind::InvalidWitness(..)));
+
+    Ok(())
+}
+
+#[rstest]
+#[case(r#"{"val": "0"}"#, vec!["0"])] // 0 => false
+#[case(r#"{"val": "1"}"#, vec!["1"])] // 1 => true
+#[case(r#"{"val": "2"}"#, vec!["0"])] // _ => false
+#[case(r#"{"val": "99"}"#, vec!["0"])]
+fn test_bit_unchecked(
+    #[case] public_inputs: &str,
+    #[case] expected_output: Vec<&str>,
+) -> Result<()> {
+    test_stdlib(
+        "bits/bit_unchecked.no",
+        None,
+        public_inputs,
+        r#"{}"#,
+        expected_output,
+    )?;
+
+    Ok(())
+}

src/tests/stdlib/mod.rs

@@ -1,3 +1,4 @@
+mod bits;
 mod comparator;
 mod mimc;
 mod multiplexer;