Move snark-gadgets to r1cs-std

r1cs-std/src/bits/uint8.rs

@@ -0,0 +1,399 @@
+use algebra::{ToConstraintField, FpParameters, Field, PrimeField};
+
+use r1cs_core::{ConstraintSystem, SynthesisError};
+
+use crate::boolean::AllocatedBit;
+use crate::fields::fp::FpGadget;
+use crate::prelude::*;
+use crate::Assignment;
+use std::borrow::Borrow;
+
+/// Represents an interpretation of 8 `Boolean` objects as an
+/// unsigned integer.
+#[derive(Clone, Debug)]
+pub struct UInt8 {
+    // Least significant bit_gadget first
+    pub(crate) bits:  Vec<Boolean>,
+    pub(crate) value: Option<u8>,
+}
+
+impl UInt8 {
+    pub fn get_value(&self) -> Option<u8> {
+        self.value
+    }
+
+    /// Construct a constant vector of `UInt8` from a vector of `u8`
+    pub fn constant_vec(values: &[u8]) -> Vec<Self> {
+        let mut result = Vec::new();
+        for value in values {
+            result.push(UInt8::constant(*value));
+        }
+        result
+    }
+
+    /// Construct a constant `UInt8` from a `u8`
+    pub fn constant(value: u8) -> Self {
+        let mut bits = Vec::with_capacity(8);
+
+        let mut tmp = value;
+        for _ in 0..8 {
+            // If last bit is one, push one.
+            if tmp & 1 == 1 {
+                bits.push(Boolean::constant(true))
+            } else {
+                bits.push(Boolean::constant(false))
+            }
+
+            tmp >>= 1;
+        }
+
+        Self {
+            bits,
+            value: Some(value),
+        }
+    }
+
+    pub fn alloc_vec<ConstraintF, CS, T>(mut cs: CS, values: &[T]) -> Result<Vec<Self>, SynthesisError>
+    where
+        ConstraintF: Field,
+        CS: ConstraintSystem<ConstraintF>,
+        T: Into<Option<u8>> + Copy,
+    {
+        let mut output_vec = Vec::with_capacity(values.len());
+        for (i, value) in values.into_iter().enumerate() {
+            let byte: Option<u8> = Into::into(*value);
+            let alloc_byte = Self::alloc(&mut cs.ns(|| format!("byte_{}", i)), || byte.get())?;
+            output_vec.push(alloc_byte);
+        }
+        Ok(output_vec)
+    }
+
+    /// Allocates a vector of `u8`'s by first converting (chunks of) them to
+    /// `ConstraintF` elements, (thus reducing the number of input allocations), and
+    /// then converts this list of `ConstraintF` gadgets back into bytes.
+    pub fn alloc_input_vec<ConstraintF, CS>(mut cs: CS, values: &[u8]) -> Result<Vec<Self>, SynthesisError>
+    where
+        ConstraintF: PrimeField,
+        CS: ConstraintSystem<ConstraintF>,
+    {
+        let values_len = values.len();
+        let field_elements: Vec<ConstraintF> = ToConstraintField::<ConstraintF>::to_field_elements(values).unwrap();
+
+        let max_size = 8 * (ConstraintF::Params::CAPACITY / 8) as usize;
+        let mut allocated_bits = Vec::new();
+        for (i, field_element) in field_elements.into_iter().enumerate() {
+            let fe = FpGadget::alloc_input(&mut cs.ns(|| format!("Field element {}", i)), || {
+                Ok(field_element)
+            })?;
+            let mut fe_bits = fe.to_bits(cs.ns(|| format!("Convert fe to bits {}", i)))?;
+            // FpGadget::to_bits outputs a big-endian binary representation of
+            // fe_gadget's value, so we have to reverse it to get the little-endian
+            // form.
+            fe_bits.reverse();
+
+            // Remove the most significant bit, because we know it should be zero
+            // because `values.to_field_elements()` only
+            // packs field elements up to the penultimate bit.
+            // That is, the most significant bit (`ConstraintF::NUM_BITS`-th bit) is
+            // unset, so we can just pop it off.
+            allocated_bits.extend_from_slice(&fe_bits[0..max_size]);
+        }
+
+        // Chunk up slices of 8 bit into bytes.
+        Ok(allocated_bits[0..8 * values_len]
+            .chunks(8)
+            .map(Self::from_bits_le)
+            .collect())
+    }
+
+    /// Turns this `UInt8` into its little-endian byte order representation.
+    /// LSB-first means that we can easily get the corresponding field element
+    /// via double and add.
+    pub fn into_bits_le(&self) -> Vec<Boolean> {
+        self.bits.iter().cloned().collect()
+    }
+
+    /// Converts a little-endian byte order representation of bits into a
+    /// `UInt8`.
+    pub fn from_bits_le(bits: &[Boolean]) -> Self {
+        assert_eq!(bits.len(), 8);
+
+        let bits = bits.to_vec();
+
+        let mut value = Some(0u8);
+        for b in bits.iter().rev() {
+            value.as_mut().map(|v| *v <<= 1);
+
+            match *b {
+                Boolean::Constant(b) => {
+                    if b {
+                        value.as_mut().map(|v| *v |= 1);
+                    }
+                },
+                Boolean::Is(ref b) => match b.get_value() {
+                    Some(true) => {
+                        value.as_mut().map(|v| *v |= 1);
+                    },
+                    Some(false) => {},
+                    None => value = None,
+                },
+                Boolean::Not(ref b) => match b.get_value() {
+                    Some(false) => {
+                        value.as_mut().map(|v| *v |= 1);
+                    },
+                    Some(true) => {},
+                    None => value = None,
+                },
+            }
+        }
+
+        Self { value, bits }
+    }
+
+    /// XOR this `UInt8` with another `UInt8`
+    pub fn xor<ConstraintF, CS>(&self, mut cs: CS, other: &Self) -> Result<Self, SynthesisError>
+    where
+        ConstraintF: Field,
+        CS: ConstraintSystem<ConstraintF>,
+    {
+        let new_value = match (self.value, other.value) {
+            (Some(a), Some(b)) => Some(a ^ b),
+            _ => None,
+        };
+
+        let bits = self
+            .bits
+            .iter()
+            .zip(other.bits.iter())
+            .enumerate()
+            .map(|(i, (a, b))| Boolean::xor(cs.ns(|| format!("xor of bit_gadget {}", i)), a, b))
+            .collect::<Result<_, _>>()?;
+
+        Ok(Self {
+            bits,
+            value: new_value,
+        })
+    }
+}
+
+impl PartialEq for UInt8 {
+    fn eq(&self, other: &Self) -> bool {
+        !self.value.is_none() && !other.value.is_none() && self.value == other.value
+    }
+}
+
+impl Eq for UInt8 {}
+
+impl<ConstraintF: Field> ConditionalEqGadget<ConstraintF> for UInt8 {
+    fn conditional_enforce_equal<CS: ConstraintSystem<ConstraintF>>(
+        &self,
+        mut cs: CS,
+        other: &Self,
+        condition: &Boolean,
+    ) -> Result<(), SynthesisError> {
+        for (i, (a, b)) in self.bits.iter().zip(&other.bits).enumerate() {
+            a.conditional_enforce_equal(
+                &mut cs.ns(|| format!("UInt8 equality check for {}-th bit", i)),
+                b,
+                condition,
+            )?;
+        }
+        Ok(())
+    }
+
+    fn cost() -> usize {
+        8 * <Boolean as ConditionalEqGadget<ConstraintF>>::cost()
+    }
+}
+
+impl<ConstraintF: Field> EqGadget<ConstraintF> for UInt8 {}
+
+impl<ConstraintF: Field> AllocGadget<u8, ConstraintF> for UInt8 {
+    fn alloc<F, T, CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        value_gen: F,
+    ) -> Result<Self, SynthesisError>
+    where
+        F: FnOnce() -> Result<T, SynthesisError>,
+        T: Borrow<u8>,
+    {
+        let value = value_gen().map(|val| *val.borrow());
+        let values = match value {
+            Ok(mut val) => {
+                let mut v = Vec::with_capacity(8);
+
+                for _ in 0..8 {
+                    v.push(Some(val & 1 == 1));
+                    val >>= 1;
+                }
+
+                v
+            },
+            _ => vec![None; 8],
+        };
+
+        let bits = values
+            .into_iter()
+            .enumerate()
+            .map(|(i, v)| {
+                Ok(Boolean::from(AllocatedBit::alloc(
+                    &mut cs.ns(|| format!("allocated bit_gadget {}", i)),
+                    || v.ok_or(SynthesisError::AssignmentMissing),
+                )?))
+            })
+            .collect::<Result<Vec<_>, SynthesisError>>()?;
+
+        Ok(Self {
+            bits,
+            value: value.ok(),
+        })
+    }
+
+    fn alloc_input<F, T, CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        value_gen: F,
+    ) -> Result<Self, SynthesisError>
+    where
+        F: FnOnce() -> Result<T, SynthesisError>,
+        T: Borrow<u8>,
+    {
+        let value = value_gen().map(|val| *val.borrow());
+        let values = match value {
+            Ok(mut val) => {
+                let mut v = Vec::with_capacity(8);
+                for _ in 0..8 {
+                    v.push(Some(val & 1 == 1));
+                    val >>= 1;
+                }
+
+                v
+            },
+            _ => vec![None; 8],
+        };
+
+        let bits = values
+            .into_iter()
+            .enumerate()
+            .map(|(i, v)| {
+                Ok(Boolean::from(AllocatedBit::alloc_input(
+                    &mut cs.ns(|| format!("allocated bit_gadget {}", i)),
+                    || v.ok_or(SynthesisError::AssignmentMissing),
+                )?))
+            })
+            .collect::<Result<Vec<_>, SynthesisError>>()?;
+
+        Ok(Self {
+            bits,
+            value: value.ok(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::UInt8;
+    use crate::{
+        bits::boolean::Boolean, test_constraint_system::TestConstraintSystem, utils::AllocGadget,
+    };
+    use algebra::fields::bls12_381::Fr;
+    use rand::{Rng, SeedableRng, XorShiftRng};
+    use r1cs_core::ConstraintSystem;
+
+    #[test]
+    fn test_uint8_from_bits_to_bits() {
+        let mut cs = TestConstraintSystem::<Fr>::new();
+        let byte_val = 0b01110001;
+        let byte = UInt8::alloc(cs.ns(|| "alloc value"), || Ok(byte_val)).unwrap();
+        let bits = byte.into_bits_le();
+        for (i, bit) in bits.iter().enumerate() {
+            assert_eq!(bit.get_value().unwrap(), (byte_val >> i) & 1 == 1)
+        }
+    }
+
+    #[test]
+    fn test_uint8_alloc_input_vec() {
+        let mut cs = TestConstraintSystem::<Fr>::new();
+        let byte_vals = (64u8..128u8).into_iter().collect::<Vec<_>>();
+        let bytes = UInt8::alloc_input_vec(cs.ns(|| "alloc value"), &byte_vals).unwrap();
+        for (native_byte, gadget_byte) in byte_vals.into_iter().zip(bytes) {
+            let bits = gadget_byte.into_bits_le();
+            for (i, bit) in bits.iter().enumerate() {
+                assert_eq!(bit.get_value().unwrap(), (native_byte >> i) & 1 == 1)
+            }
+        }
+    }
+
+    #[test]
+    fn test_uint8_from_bits() {
+        let mut rng = XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0653]);
+
+        for _ in 0..1000 {
+            let v = (0..8)
+                .map(|_| Boolean::constant(rng.gen()))
+                .collect::<Vec<_>>();
+
+            let b = UInt8::from_bits_le(&v);
+
+            for (i, bit_gadget) in b.bits.iter().enumerate() {
+                match bit_gadget {
+                    &Boolean::Constant(bit_gadget) => {
+                        assert!(bit_gadget == ((b.value.unwrap() >> i) & 1 == 1));
+                    },
+                    _ => unreachable!(),
+                }
+            }
+
+            let expected_to_be_same = b.into_bits_le();
+
+            for x in v.iter().zip(expected_to_be_same.iter()) {
+                match x {
+                    (&Boolean::Constant(true), &Boolean::Constant(true)) => {},
+                    (&Boolean::Constant(false), &Boolean::Constant(false)) => {},
+                    _ => unreachable!(),
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_uint8_xor() {
+        let mut rng = XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0653]);
+
+        for _ in 0..1000 {
+            let mut cs = TestConstraintSystem::<Fr>::new();
+
+            let a: u8 = rng.gen();
+            let b: u8 = rng.gen();
+            let c: u8 = rng.gen();
+
+            let mut expected = a ^ b ^ c;
+
+            let a_bit = UInt8::alloc(cs.ns(|| "a_bit"), || Ok(a)).unwrap();
+            let b_bit = UInt8::constant(b);
+            let c_bit = UInt8::alloc(cs.ns(|| "c_bit"), || Ok(c)).unwrap();
+
+            let r = a_bit.xor(cs.ns(|| "first xor"), &b_bit).unwrap();
+            let r = r.xor(cs.ns(|| "second xor"), &c_bit).unwrap();
+
+            assert!(cs.is_satisfied());
+
+            assert!(r.value == Some(expected));
+
+            for b in r.bits.iter() {
+                match b {
+                    &Boolean::Is(ref b) => {
+                        assert!(b.get_value().unwrap() == (expected & 1 == 1));
+                    },
+                    &Boolean::Not(ref b) => {
+                        assert!(!b.get_value().unwrap() == (expected & 1 == 1));
+                    },
+                    &Boolean::Constant(b) => {
+                        assert!(b == (expected & 1 == 1));
+                    },
+                }
+
+                expected >>= 1;
+            }
+        }
+    }
+}