makes API cmp-like

r1cs-std/src/smaller_than.rs → r1cs-std/src/cmp.rs

@@ -5,83 +5,144 @@ use crate::{
 };
 use algebra::PrimeField;
 use r1cs_core::{ConstraintSystem, SynthesisError};
-use std::marker::PhantomData;
+use std::{
+    cmp::Ordering,
+    marker::PhantomData
+};
 
-pub struct SmallerThanGadget<ConstraintF: PrimeField> {
+pub struct CmpGadget<ConstraintF: PrimeField> {
     constraint_field_type: PhantomData<ConstraintF>,
 }
 
-impl<ConstraintF: PrimeField> SmallerThanGadget<ConstraintF> {
-    // the function assumes a and b are known to be <= (p-1)/2
-    pub fn is_smaller_than<CS: ConstraintSystem<ConstraintF>>(
+impl<ConstraintF: PrimeField> CmpGadget<ConstraintF> {
+    fn process_cmp_inputs<CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        a: &FpGadget<ConstraintF>,
+        b: &FpGadget<ConstraintF>,
+        ordering: Ordering,
+        should_also_check_equality: bool,
+    ) -> Result<(FpGadget<ConstraintF>, FpGadget<ConstraintF>), SynthesisError> {
+        let left;
+        let right;
+        match ordering {
+            Ordering::Less => { left = a; right = b; }
+            Ordering::Greater => {left = b; right = a; }
+            Ordering::Equal => { return Err(SynthesisError::Unsatisfiable); }
+        };
+        let right_for_check = if should_also_check_equality {
+            right.add_constant(cs.ns(|| "plus one"), &ConstraintF::one())?
+        } else {
+            right.clone()
+        };
+
+        Ok((left.clone(), right_for_check))
+    }
+
+    fn check_smaller_than_mod_minus_one_div_two<CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        a: &FpGadget<ConstraintF>,
+    ) -> Result<(), SynthesisError>  {
+        let a_bits = a.to_bits(cs.ns(|| "a to bits"))?;
+        Boolean::enforce_smaller_or_equal_than::<_, _, ConstraintF, _>(
+            cs.ns(|| "enforce smaller than modulus minus one div two"),
+            &a_bits,
+            ConstraintF::modulus_minus_one_div_two(),
+        )?;
+
+        Ok(())
+    }
+
+    /// this function verifies a and b are <= (p-1)/2
+    pub fn enforce_cmp<CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        a: &FpGadget<ConstraintF>,
+        b: &FpGadget<ConstraintF>,
+        ordering: Ordering,
+        should_also_check_equality: bool,
+    ) -> Result<(), SynthesisError> {
+        let (left, right) = Self::process_cmp_inputs(cs.ns(|| "process cmp inputs"), a, b, ordering, should_also_check_equality)?;
+        Self::enforce_smaller_than_unchecked(cs.ns(|| "enforce smaller than"), &left, &right)
+    }
+
+    /// this function assumes a and b are known to be <= (p-1)/2
+    pub fn enforce_cmp_unchecked<CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        a: &FpGadget<ConstraintF>,
+        b: &FpGadget<ConstraintF>,
+        ordering: Ordering,
+        should_also_check_equality: bool,
+    ) -> Result<(), SynthesisError> {
+        let (left, right) = Self::process_cmp_inputs(cs.ns(|| "process cmp inputs"), a, b, ordering, should_also_check_equality)?;
+        Self::enforce_smaller_than(cs.ns(|| "enforce smaller than"), &left, &right)
+    }
+
+    /// this function verifies a and b are <= (p-1)/2
+    pub fn is_cmp<CS: ConstraintSystem<ConstraintF>>(
         mut cs: CS,
         a: &FpGadget<ConstraintF>,
         b: &FpGadget<ConstraintF>,
+        ordering: Ordering,
+        should_also_check_equality: bool,
     ) -> Result<Boolean, SynthesisError> {
-        let two = ConstraintF::one() + ConstraintF::one();
-        let d0 = a.sub(cs.ns(|| "a - b"), b)?;
-        let d = d0.mul_by_constant(cs.ns(|| "mul 2"), &two)?;
-        let d_bits = d.to_bits_strict(cs.ns(|| "d to bits"))?;
-        let d_bits_len = d_bits.len();
-        Ok(d_bits[d_bits_len - 1])
+        let (left, right) = Self::process_cmp_inputs(cs.ns(|| "process cmp inputs"), a, b, ordering, should_also_check_equality)?;
+        Self::is_smaller_than(cs.ns(|| "enforce smaller than"), &left, &right)
     }
 
-    // the function assumes a and b are known to be <= (p-1)/2
-    pub fn is_smaller_than_or_equal_to<CS: ConstraintSystem<ConstraintF>>(
+    /// this function assumes a and b are known to be <= (p-1)/2
+    pub fn is_cmp_unchecked<CS: ConstraintSystem<ConstraintF>>(
         mut cs: CS,
         a: &FpGadget<ConstraintF>,
         b: &FpGadget<ConstraintF>,
+        ordering: Ordering,
+        should_also_check_equality: bool,
     ) -> Result<Boolean, SynthesisError> {
-        let b_plus_one = b.add_constant(cs.ns(|| "plus one"), &ConstraintF::one())?;
-        Self::is_smaller_than(cs.ns(|| "is smaller than"), a, &b_plus_one)
+        let (left, right) = Self::process_cmp_inputs(cs.ns(|| "process cmp inputs"), a, b, ordering, should_also_check_equality)?;
+        Self::is_smaller_than_unchecked(cs.ns(|| "enforce smaller than"), &left, &right)
     }
 
-    // the function assumes a and b are known to be <= (p-1)/2
-    pub fn enforce_smaller_than<CS: ConstraintSystem<ConstraintF>>(
+    /// this function verifies a and b are <= (p-1)/2
+    fn is_smaller_than<CS: ConstraintSystem<ConstraintF>>(
         mut cs: CS,
         a: &FpGadget<ConstraintF>,
         b: &FpGadget<ConstraintF>,
-    ) -> Result<(), SynthesisError> {
-        let is_smaller_than = Self::is_smaller_than(cs.ns(|| "is smaller than"), a, b)?;
-        cs.enforce(
-            || "enforce smaller than",
-            |_| is_smaller_than.lc(CS::one(), ConstraintF::one()),
-            |lc| lc + (ConstraintF::one(), CS::one()),
-            |lc| lc + (ConstraintF::one(), CS::one()),
-        );
+    ) -> Result<Boolean, SynthesisError> {
+        Self::check_smaller_than_mod_minus_one_div_two(cs.ns(|| "check a in range"), a)?;
+        Self::check_smaller_than_mod_minus_one_div_two(cs.ns(|| "check b in range"), b)?;
+        Self::is_smaller_than_unchecked(cs.ns(|| "enforce smaller than"), a, b)
+    }
 
-        Ok(())
+    /// this function assumes a and b are known to be <= (p-1)/2
+    fn is_smaller_than_unchecked<CS: ConstraintSystem<ConstraintF>>(
+        mut cs: CS,
+        a: &FpGadget<ConstraintF>,
+        b: &FpGadget<ConstraintF>,
+    ) -> Result<Boolean, SynthesisError> {
+        let two = ConstraintF::one() + ConstraintF::one();
+        let d0 = a.sub(cs.ns(|| "a - b"), b)?;
+        let d = d0.mul_by_constant(cs.ns(|| "mul 2"), &two)?;
+        let d_bits = d.to_bits_strict(cs.ns(|| "d to bits"))?;
+        let d_bits_len = d_bits.len();
+        Ok(d_bits[d_bits_len - 1])
     }
 
-    // the function assumes a and b are known to be <= (p-1)/2
-    pub fn enforce_smaller_than_or_equal_to<CS: ConstraintSystem<ConstraintF>>(
+    /// this function verifies a and b are <= (p-1)/2
+    fn enforce_smaller_than<CS: ConstraintSystem<ConstraintF>>(
         mut cs: CS,
         a: &FpGadget<ConstraintF>,
         b: &FpGadget<ConstraintF>,
     ) -> Result<(), SynthesisError> {
-        let b_plus_one = b.add_constant(cs.ns(|| "plus one"), &ConstraintF::one())?;
-        Self::enforce_smaller_than(cs.ns(|| "enforce smaller than"), a, &b_plus_one)
+        Self::check_smaller_than_mod_minus_one_div_two(cs.ns(|| "check a in range"), a)?;
+        Self::check_smaller_than_mod_minus_one_div_two(cs.ns(|| "check b in range"), b)?;
+        Self::enforce_smaller_than_unchecked(cs.ns(|| "enforce smaller than"), a, b)
     }
 
-    pub fn enforce_smaller_than_strict<CS: ConstraintSystem<ConstraintF>>(
+    /// this function assumes a and b are known to be <= (p-1)/2
+    fn enforce_smaller_than_unchecked<CS: ConstraintSystem<ConstraintF>>(
         mut cs: CS,
         a: &FpGadget<ConstraintF>,
         b: &FpGadget<ConstraintF>,
     ) -> Result<(), SynthesisError> {
-        let a_bits = a.to_bits(cs.ns(|| "a to bits"))?;
-        Boolean::enforce_smaller_or_equal_than::<_, _, ConstraintF, _>(
-            cs.ns(|| "enforce a smaller than modulus minus one div two"),
-            &a_bits,
-            ConstraintF::modulus_minus_one_div_two(),
-        )?;
-        let b_bits = b.to_bits(cs.ns(|| "b to bits"))?;
-        Boolean::enforce_smaller_or_equal_than::<_, _, ConstraintF, _>(
-            cs.ns(|| "enforce b smaller than modulus minus one div two"),
-            &b_bits,
-            ConstraintF::modulus_minus_one_div_two(),
-        )?;
-
-        let is_smaller_than = Self::is_smaller_than(cs.ns(|| "is smaller than"), a, b)?;
+        let is_smaller_than = Self::is_smaller_than_unchecked(cs.ns(|| "is smaller than"), a, b)?;
         cs.enforce(
             || "enforce smaller than",
             |_| is_smaller_than.lc(CS::one(), ConstraintF::one()),
@@ -91,15 +152,6 @@ impl SmallerThanGadget {
 
         Ok(())
     }
-
-    pub fn enforce_smaller_than_or_equal_to_strict<CS: ConstraintSystem<ConstraintF>>(
-        mut cs: CS,
-        a: &FpGadget<ConstraintF>,
-        b: &FpGadget<ConstraintF>,
-    ) -> Result<(), SynthesisError> {
-        let b_plus_one = b.add_constant(cs.ns(|| "plus one"), &ConstraintF::one())?;
-        Self::enforce_smaller_than_strict(cs.ns(|| "enforce smaller than strict"), a, &b_plus_one)
-    }
 }
 
 #[cfg(test)]
@@ -108,7 +160,7 @@ mod test {
     use rand_xorshift::XorShiftRng;
     use std::cmp::Ordering;
 
-    use super::SmallerThanGadget;
+    use super::CmpGadget;
     use crate::{
         alloc::AllocGadget, fields::fp::FpGadget, test_constraint_system::TestConstraintSystem,
     };
@@ -141,30 +193,38 @@ mod test {
 
             match a.cmp(&b) {
                 Ordering::Less => {
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test"),
                         &a_var,
                         &b_var,
+                        Ordering::Less,
+                        false,
                     )
                     .unwrap();
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_or_equal_to_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test 2"),
                         &a_var,
                         &b_var,
+                        Ordering::Less,
+                        true,
                     )
                     .unwrap();
                 },
                 Ordering::Greater => {
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test"),
-                        &b_var,
                         &a_var,
+                        &b_var,
+                        Ordering::Greater,
+                        false,
                     )
                     .unwrap();
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_or_equal_to_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test 2"),
-                        &b_var,
                         &a_var,
+                        &b_var,
+                        Ordering::Greater,
+                        true,
                     )
                     .unwrap();
                 },
@@ -186,30 +246,38 @@ mod test {
 
             match b.cmp(&a) {
                 Ordering::Less => {
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test"),
                         &a_var,
                         &b_var,
+                        Ordering::Less,
+                        false,
                     )
                     .unwrap();
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_or_equal_to_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test 2"),
                         &a_var,
                         &b_var,
+                        Ordering::Less,
+                        true,
                     )
                     .unwrap();
                 },
                 Ordering::Greater => {
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_strict(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test"),
-                        &b_var,
                         &a_var,
+                        &b_var,
+                        Ordering::Greater,
+                        false,
                     )
                     .unwrap();
-                    SmallerThanGadget::<Fr>::enforce_smaller_than_or_equal_to(
+                    CmpGadget::<Fr>::enforce_cmp(
                         cs.ns(|| "smaller than test 2"),
-                        &b_var,
                         &a_var,
+                        &b_var,
+                        Ordering::Greater,
+                        true,
                     )
                     .unwrap();
                 },
@@ -223,10 +291,12 @@ mod test {
             let mut cs = TestConstraintSystem::<Fr>::new();
             let a = rand_in_range(&mut rng);
             let a_var = FpGadget::<Fr>::alloc(cs.ns(|| "a"), || Ok(a)).unwrap();
-            SmallerThanGadget::<Fr>::enforce_smaller_than_strict(
+            CmpGadget::<Fr>::enforce_cmp(
                 cs.ns(|| "smaller than test"),
                 &a_var,
                 &a_var,
+                Ordering::Less,
+                false,
             )
             .unwrap();
 
@@ -237,10 +307,12 @@ mod test {
             let mut cs = TestConstraintSystem::<Fr>::new();
             let a = rand_in_range(&mut rng);
             let a_var = FpGadget::<Fr>::alloc(cs.ns(|| "a"), || Ok(a)).unwrap();
-            SmallerThanGadget::<Fr>::enforce_smaller_than_or_equal_to(
+            CmpGadget::<Fr>::enforce_cmp(
                 cs.ns(|| "smaller than or equal to test"),
                 &a_var,
                 &a_var,
+                Ordering::Less,
+                true,
             )
             .unwrap();
 

r1cs-std/src/lib.rs

@@ -62,7 +62,7 @@ pub mod pairing;
 pub mod alloc;
 pub mod eq;
 pub mod select;
-pub mod smaller_than;
+pub mod cmp;
 
 pub mod prelude {
     pub use crate::{
@@ -74,6 +74,7 @@ pub mod prelude {
         instantiated::*,
         pairing::PairingGadget,
         select::*,
+        cmp::CmpGadget,
     };
 }