Experimental features

Cargo.toml

@@ -87,4 +87,4 @@ ark-mnt4-753 = { git = "https://github.com/arkworks-rs/curves/" }
 ark-mnt6-298 = { git = "https://github.com/arkworks-rs/curves/" }
 ark-mnt6-753 = { git = "https://github.com/arkworks-rs/curves/" }
 ark-pallas = { git = "https://github.com/arkworks-rs/curves/" }
-ark-relations = { git = "https://github.com/winderica/snark/", branch = "cp" }
+ark-relations = { git = "https://github.com/winderica/snark/", branch = "experimental" }

src/alloc.rs

@@ -1,7 +1,7 @@
-use crate::Vec;
 use ark_ff::Field;
 use ark_relations::r1cs::{Namespace, SynthesisError};
 use core::borrow::Borrow;
+use ark_std::vec::Vec;
 
 /// Describes the mode that a variable should be allocated in within
 /// a `ConstraintSystem`.

src/boolean/allocated.rs

@@ -1,4 +1,4 @@
-use core::borrow::Borrow;
+use core::borrow::{Borrow, BorrowMut};
 
 use ark_ff::{Field, PrimeField};
 use ark_relations::r1cs::{ConstraintSystemRef, Namespace, SynthesisError, Variable};
@@ -6,7 +6,6 @@ use ark_relations::r1cs::{ConstraintSystemRef, Namespace, SynthesisError, Variab
 use crate::{
     alloc::{AllocVar, AllocationMode},
     select::CondSelectGadget,
-    Assignment,
 };
 
 use super::Boolean;
@@ -22,23 +21,14 @@ use super::Boolean;
 pub struct AllocatedBool<F: Field> {
     pub(super) variable: Variable,
     pub(super) cs: ConstraintSystemRef<F>,
-}
-
-pub(crate) fn bool_to_field<F: Field>(val: impl Borrow<bool>) -> F {
-    F::from(*val.borrow())
+    pub(super) enable_lc: bool,
+    pub(super) value: Option<bool>,
 }
 
 impl<F: Field> AllocatedBool<F> {
     /// Get the assigned value for `self`.
     pub fn value(&self) -> Result<bool, SynthesisError> {
-        let value = self.cs.assigned_value(self.variable).get()?;
-        if value.is_zero() {
-            Ok(false)
-        } else if value.is_one() {
-            Ok(true)
-        } else {
-            unreachable!("Incorrect value assigned: {:?}", value);
-        }
+        self.value.ok_or(SynthesisError::AssignmentMissing)
     }
 
     /// Get the R1CS variable for `self`.
@@ -52,18 +42,29 @@ impl AllocatedBool {
         cs: ConstraintSystemRef<F>,
         f: impl FnOnce() -> Result<T, SynthesisError>,
     ) -> Result<Self, SynthesisError> {
-        let variable = cs.new_witness_variable(|| f().map(bool_to_field))?;
-        Ok(Self { variable, cs })
+        let value = f().map(|b| *b.borrow());
+        Ok(Self {
+            variable: cs.new_witness_variable(|| value.map(F::from))?,
+            enable_lc: cs.should_construct_matrices(),
+            cs,
+            value: value.ok(),
+        })
     }
 
     /// Performs an XOR operation over the two operands, returning
     /// an `AllocatedBool`.
     #[tracing::instrument(target = "r1cs")]
     pub fn not(&self) -> Result<Self, SynthesisError> {
-        let variable = self.cs.new_lc(lc!() + Variable::One - self.variable)?;
+        let variable = self.cs.new_lc(if self.enable_lc {
+            lc!() + Variable::One - self.variable
+        } else {
+            lc!()
+        })?;
         Ok(Self {
             variable,
             cs: self.cs.clone(),
+            value: self.value.map(|v| !v),
+            enable_lc: self.cs.should_construct_matrices()
         })
     }
 
@@ -90,11 +91,15 @@ impl AllocatedBool {
         // -2a * b = c - a - b
         // 2a * b = a + b - c
         // (a + a) * b = a + b - c
-        self.cs.enforce_constraint(
-            lc!() + self.variable + self.variable,
-            lc!() + b.variable,
-            lc!() + self.variable + b.variable - result.variable,
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable + self.variable,
+                lc!() + b.variable,
+                lc!() + self.variable + b.variable - result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -109,11 +114,15 @@ impl AllocatedBool {
 
         // Constrain (a) * (b) = (c), ensuring c is 1 iff
         // a AND b are both 1.
-        self.cs.enforce_constraint(
-            lc!() + self.variable,
-            lc!() + b.variable,
-            lc!() + result.variable,
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable,
+                lc!() + b.variable,
+                lc!() + result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -128,11 +137,15 @@ impl AllocatedBool {
 
         // Constrain (1 - a) * (1 - b) = (1 - c), ensuring c is 0 iff
         // a and b are both false, and otherwise c is 1.
-        self.cs.enforce_constraint(
-            lc!() + Variable::One - self.variable,
-            lc!() + Variable::One - b.variable,
-            lc!() + Variable::One - result.variable,
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + Variable::One - self.variable,
+                lc!() + Variable::One - b.variable,
+                lc!() + Variable::One - result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -146,11 +159,15 @@ impl AllocatedBool {
 
         // Constrain (a) * (1 - b) = (c), ensuring c is 1 iff
         // a is true and b is false, and otherwise c is 0.
-        self.cs.enforce_constraint(
-            lc!() + self.variable,
-            lc!() + Variable::One - b.variable,
-            lc!() + result.variable,
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable,
+                lc!() + Variable::One - b.variable,
+                lc!() + result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -164,11 +181,15 @@ impl AllocatedBool {
 
         // Constrain (1 - a) * (1 - b) = (c), ensuring c is 1 iff
         // a and b are both false, and otherwise c is 0.
-        self.cs.enforce_constraint(
-            lc!() + Variable::One - self.variable,
-            lc!() + Variable::One - b.variable,
-            lc!() + result.variable,
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + Variable::One - self.variable,
+                lc!() + Variable::One - b.variable,
+                lc!() + result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -189,25 +210,37 @@ impl AllocVar for AllocatedBool {
         let ns = cs.into();
         let cs = ns.cs();
         if mode == AllocationMode::Constant {
-            let variable = if *f()?.borrow() {
-                Variable::One
-            } else {
-                Variable::Zero
-            };
-            Ok(Self { variable, cs })
+            let value = *f()?.borrow();
+            Ok(Self {
+                variable: if value { Variable::One } else { Variable::Zero },
+                enable_lc: cs.should_construct_matrices(),
+                cs,
+                value: Some(value),
+            })
         } else {
+            let value = f().map(|b| *b.borrow());
             let variable = if mode == AllocationMode::Input {
-                cs.new_input_variable(|| f().map(bool_to_field))?
+                cs.new_input_variable(|| value.map(F::from))?
             } else {
-                cs.new_witness_variable(|| f().map(bool_to_field))?
+                cs.new_witness_variable(|| value.map(F::from))?
             };
 
+            let enable_lc = cs.should_construct_matrices();
+
             // Constrain: (1 - a) * a = 0
             // This constrains a to be either 0 or 1.
+            if enable_lc {
+                cs.enforce_constraint(lc!() + Variable::One - variable, lc!() + variable, lc!())?;
+            } else {
+                cs.borrow_mut().unwrap().num_constraints += 1;
+            }
 
-            cs.enforce_constraint(lc!() + Variable::One - variable, lc!() + variable, lc!())?;
-
-            Ok(Self { variable, cs })
+            Ok(Self {
+                variable,
+                enable_lc,
+                cs,
+                value: value.ok(),
+            })
         }
     }
 }

src/boolean/eq.rs

@@ -1,7 +1,6 @@
 use ark_relations::r1cs::SynthesisError;
 
-use crate::boolean::Boolean;
-use crate::eq::EqGadget;
+use crate::{boolean::Boolean, eq::EqGadget};
 
 use super::*;
 
@@ -26,24 +25,46 @@ impl EqGadget for Boolean {
         use Boolean::*;
         let one = Variable::One;
         // We will use the following trick: a == b <=> a - b == 0
-        // This works because a - b == 0 if and only if a = 0 and b = 0, or a = 1 and b = 1,
-        // which is exactly the definition of a == b.
+        // This works because a - b == 0 if and only if a = 0 and b = 0, or a = 1 and b
+        // = 1, which is exactly the definition of a == b.
         let difference = match (self, other) {
             // 1 == 1; 0 == 0
             (Constant(true), Constant(true)) | (Constant(false), Constant(false)) => return Ok(()),
             // false != true
             (Constant(_), Constant(_)) => return Err(SynthesisError::Unsatisfiable),
             // 1 - a
-            (Constant(true), Var(a)) | (Var(a), Constant(true)) => lc!() + one - a.variable(),
+            (Constant(true), Var(a)) | (Var(a), Constant(true)) => {
+                if a.enable_lc {
+                    lc!() + one - a.variable()
+                } else {
+                    lc!()
+                }
+            },
             // a - 0 = a
-            (Constant(false), Var(a)) | (Var(a), Constant(false)) => lc!() + a.variable(),
+            (Constant(false), Var(a)) | (Var(a), Constant(false)) => {
+                if a.enable_lc {
+                    lc!() + a.variable()
+                } else {
+                    lc!()
+                }
+            },
             // b - a,
-            (Var(a), Var(b)) => lc!() + b.variable() - a.variable(),
+            (Var(a), Var(b)) => {
+                if a.enable_lc || b.enable_lc {
+                    lc!() + b.variable() - a.variable()
+                } else {
+                    lc!()
+                }
+            },
         };
 
         if condition != &Constant(false) {
             let cs = self.cs().or(other.cs()).or(condition.cs());
-            cs.enforce_constraint(lc!() + difference, condition.lc(), lc!())?;
+            if cs.should_construct_matrices() {
+                cs.enforce_constraint(lc!() + difference, condition.lc(), lc!())?;
+            } else {
+                cs.borrow_mut().unwrap().num_constraints += 1;
+            }
         }
         Ok(())
     }
@@ -57,24 +78,46 @@ impl EqGadget for Boolean {
         use Boolean::*;
         let one = Variable::One;
         // We will use the following trick: a != b <=> a + b == 1
-        // This works because a + b == 1 if and only if a = 0 and b = 1, or a = 1 and b = 0,
-        // which is exactly the definition of a != b.
+        // This works because a + b == 1 if and only if a = 0 and b = 1, or a = 1 and b
+        // = 0, which is exactly the definition of a != b.
         let sum = match (self, other) {
             // 1 != 0; 0 != 1
             (Constant(true), Constant(false)) | (Constant(false), Constant(true)) => return Ok(()),
             // false == false and true == true
             (Constant(_), Constant(_)) => return Err(SynthesisError::Unsatisfiable),
             // 1 + a
-            (Constant(true), Var(a)) | (Var(a), Constant(true)) => lc!() + one + a.variable(),
+            (Constant(true), Var(a)) | (Var(a), Constant(true)) => {
+                if a.enable_lc {
+                    lc!() + one + a.variable()
+                } else {
+                    lc!()
+                }
+            },
             // a + 0 = a
-            (Constant(false), Var(a)) | (Var(a), Constant(false)) => lc!() + a.variable(),
+            (Constant(false), Var(a)) | (Var(a), Constant(false)) => {
+                if a.enable_lc {
+                    lc!() + a.variable()
+                } else {
+                    lc!()
+                }
+            },
             // b + a,
-            (Var(a), Var(b)) => lc!() + b.variable() + a.variable(),
+            (Var(a), Var(b)) => {
+                if a.enable_lc || b.enable_lc {
+                    lc!() + b.variable() + a.variable()
+                } else {
+                    lc!()
+                }
+            },
         };
 
         if should_enforce != &Constant(false) {
             let cs = self.cs().or(other.cs()).or(should_enforce.cs());
-            cs.enforce_constraint(sum, should_enforce.lc(), lc!() + one)?;
+            if cs.should_construct_matrices() {
+                cs.enforce_constraint(sum, should_enforce.lc(), lc!() + one)?;
+            } else {
+                cs.borrow_mut().unwrap().num_constraints += 1;
+            }
         }
         Ok(())
     }

src/boolean/select.rs

@@ -78,11 +78,15 @@ impl CondSelectGadget for Boolean {
                     //   0  |   1   |   0  |    1
                     //   1  |   0   |   0  |    0
                     //   1  |   1   |   0  |    1
-                    cs.enforce_constraint(
-                        cond.lc(),
-                        lc!() + a.lc() - b.lc(),
-                        lc!() + result.lc() - b.lc(),
-                    )?;
+                    if cs.should_construct_matrices() {
+                        cs.enforce_constraint(
+                            cond.lc(),
+                            lc!() + a.lc() - b.lc(),
+                            lc!() + result.lc() - b.lc(),
+                        )?;
+                    } else {
+                        cs.borrow_mut().unwrap().num_constraints += 1;
+                    }
 
                     Ok(result)
                 },

src/eq.rs

@@ -123,11 +123,16 @@ impl + R1CSVar, F: PrimeField> EqGadget for [T] {
             Ok(())
         } else {
             let cs = [&some_are_different, should_enforce].cs();
-            cs.enforce_constraint(
-                some_are_different.lc(),
-                should_enforce.lc(),
-                should_enforce.lc(),
-            )
+            if cs.should_construct_matrices() {
+                cs.enforce_constraint(
+                    some_are_different.lc(),
+                    should_enforce.lc(),
+                    should_enforce.lc(),
+                )?;
+            } else {
+                cs.borrow_mut().unwrap().num_constraints += 1;
+            }
+            Ok(())
         }
     }
 }

src/fields/fp/cmp.rs

@@ -144,10 +144,14 @@ impl FpVar {
     /// verify that.
     fn enforce_smaller_than_unchecked(&self, other: &FpVar<F>) -> Result<(), SynthesisError> {
         let is_smaller_than = self.is_smaller_than_unchecked(other)?;
-        let lc_one = lc!() + Variable::One;
-        [self, other]
-            .cs()
-            .enforce_constraint(is_smaller_than.lc(), lc_one.clone(), lc_one)
+        let cs = [self, other].cs();
+        if cs.should_construct_matrices() {
+            let lc_one = lc!() + Variable::One;
+            cs.enforce_constraint(is_smaller_than.lc(), lc_one.clone(), lc_one)?;
+        } else {
+            cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+        Ok(())
     }
 }
 

src/fields/fp/mod.rs

@@ -26,6 +26,7 @@ pub struct AllocatedFp {
     pub variable: Variable,
     /// The constraint system that `self` was allocated in.
     pub cs: ConstraintSystemRef<F>,
+    enable_lc: bool,
 }
 
 impl<F: PrimeField> AllocatedFp<F> {
@@ -35,6 +36,7 @@ impl AllocatedFp {
         Self {
             value,
             variable,
+            enable_lc: cs.should_construct_matrices(),
             cs,
         }
     }
@@ -52,7 +54,8 @@ pub enum FpVar {
 }
 
 impl<F: PrimeField> FpVar<F> {
-    /// Decomposes `self` into a vector of `bits` and a remainder `rest` such that
+    /// Decomposes `self` into a vector of `bits` and a remainder `rest` such
+    /// that
     /// * `bits.len() == size`, and
     /// * `rest == 0`.
     pub fn to_bits_le_with_top_bits_zero(
@@ -105,7 +108,11 @@ impl From> for FpVar {
         } else {
             // `other` is a variable
             let cs = other.cs();
-            let variable = cs.new_lc(other.lc()).unwrap();
+            let variable = cs.new_lc(if cs.should_construct_matrices() {
+                other.lc()
+            } else {
+                lc!()
+            }).unwrap();
             Self::Var(AllocatedFp::new(
                 other.value().ok().map(|b| F::from(b as u8)),
                 variable,
@@ -129,14 +136,18 @@ impl AllocatedFp {
     /// `zero`, else it outputs `one`.
     pub fn from(other: Boolean<F>) -> Self {
         let cs = other.cs();
-        let variable = cs.new_lc(other.lc()).unwrap();
+        let variable = cs.new_lc(if cs.should_construct_matrices() {
+            other.lc()
+        } else {
+            lc!()
+        }).unwrap();
         Self::new(other.value().ok().map(|b| F::from(b as u8)), variable, cs)
     }
 
     /// Returns the value assigned to `self` in the underlying constraint system
     /// (if a value was assigned).
     pub fn value(&self) -> Result<F, SynthesisError> {
-        self.cs.assigned_value(self.variable).get()
+        self.value.ok_or(SynthesisError::AssignmentMissing)
     }
 
     /// Outputs `self + other`.
@@ -151,7 +162,11 @@ impl AllocatedFp {
 
         let variable = self
             .cs
-            .new_lc(lc!() + self.variable + other.variable)
+            .new_lc(if self.enable_lc {
+                lc!() + self.variable + other.variable
+            } else {
+                lc!()
+            })
             .unwrap();
         AllocatedFp::new(value, variable, self.cs.clone())
     }
@@ -177,7 +192,9 @@ impl AllocatedFp {
             } else {
                 value += variable.value.unwrap();
             }
-            new_lc = new_lc + variable.variable;
+            if variable.enable_lc {
+                new_lc = new_lc + variable.variable;
+            }
             num_iters += 1;
         }
         assert_ne!(num_iters, 0);
@@ -203,7 +220,11 @@ impl AllocatedFp {
 
         let variable = self
             .cs
-            .new_lc(lc!() + self.variable - other.variable)
+            .new_lc(if self.enable_lc {
+                lc!() + self.variable - other.variable
+            } else {
+                lc!()
+            })
             .unwrap();
         AllocatedFp::new(value, variable, self.cs.clone())
     }
@@ -217,13 +238,18 @@ impl AllocatedFp {
             Ok(self.value.get()? * &other.value.get()?)
         })
         .unwrap();
-        self.cs
-            .enforce_constraint(
-                lc!() + self.variable,
-                lc!() + other.variable,
-                lc!() + product.variable,
-            )
-            .unwrap();
+        if self.enable_lc {
+            self.cs
+                .enforce_constraint(
+                    lc!() + self.variable,
+                    lc!() + other.variable,
+                    lc!() + product.variable,
+                )
+                .unwrap();
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+
         product
     }
 
@@ -238,7 +264,11 @@ impl AllocatedFp {
             let value = self.value.map(|val| val + other);
             let variable = self
                 .cs
-                .new_lc(lc!() + self.variable + (other, Variable::One))
+                .new_lc(if self.enable_lc {
+                    lc!() + self.variable + (other, Variable::One)
+                } else {
+                    lc!()
+                })
                 .unwrap();
             AllocatedFp::new(value, variable, self.cs.clone())
         }
@@ -261,7 +291,14 @@ impl AllocatedFp {
             self.clone()
         } else {
             let value = self.value.map(|val| val * other);
-            let variable = self.cs.new_lc(lc!() + (other, self.variable)).unwrap();
+            let variable = self
+                .cs
+                .new_lc(if self.enable_lc {
+                    lc!() + (other, self.variable)
+                } else {
+                    lc!()
+                })
+                .unwrap();
             AllocatedFp::new(value, variable, self.cs.clone())
         }
     }
@@ -272,7 +309,11 @@ impl AllocatedFp {
     #[tracing::instrument(target = "r1cs")]
     pub fn double(&self) -> Result<Self, SynthesisError> {
         let value = self.value.map(|val| val.double());
-        let variable = self.cs.new_lc(lc!() + self.variable + self.variable)?;
+        let variable = self.cs.new_lc(if self.enable_lc {
+            lc!() + self.variable + self.variable
+        } else {
+            lc!()
+        })?;
         Ok(Self::new(value, variable, self.cs.clone()))
     }
 
@@ -294,7 +335,14 @@ impl AllocatedFp {
         if let Some(val) = self.value.as_mut() {
             *val = -(*val);
         }
-        self.variable = self.cs.new_lc(lc!() - self.variable).unwrap();
+        self.variable = self
+            .cs
+            .new_lc(if self.enable_lc {
+                lc!() - self.variable
+            } else {
+                lc!()
+            })
+            .unwrap();
         self
     }
 
@@ -315,11 +363,16 @@ impl AllocatedFp {
             Ok(self.value.get()?.inverse().unwrap_or_else(F::zero))
         })?;
 
-        self.cs.enforce_constraint(
-            lc!() + self.variable,
-            lc!() + inverse.variable,
-            lc!() + Variable::One,
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable,
+                lc!() + inverse.variable,
+                lc!() + Variable::One,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+
         Ok(inverse)
     }
 
@@ -334,11 +387,16 @@ impl AllocatedFp {
     /// This requires *one* constraint.
     #[tracing::instrument(target = "r1cs")]
     pub fn mul_equals(&self, other: &Self, result: &Self) -> Result<(), SynthesisError> {
-        self.cs.enforce_constraint(
-            lc!() + self.variable,
-            lc!() + other.variable,
-            lc!() + result.variable,
-        )
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable,
+                lc!() + other.variable,
+                lc!() + result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+        Ok(())
     }
 
     /// Enforces that `self * self = result`.
@@ -346,11 +404,16 @@ impl AllocatedFp {
     /// This requires *one* constraint.
     #[tracing::instrument(target = "r1cs")]
     pub fn square_equals(&self, result: &Self) -> Result<(), SynthesisError> {
-        self.cs.enforce_constraint(
-            lc!() + self.variable,
-            lc!() + self.variable,
-            lc!() + result.variable,
-        )
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable,
+                lc!() + self.variable,
+                lc!() + result.variable,
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+        Ok(())
     }
 
     /// Outputs the bit `self == other`.
@@ -424,16 +487,20 @@ impl AllocatedFp {
         // and constraint 2 enforces that if self != other, then `is_not_equal = 1`.
         // Since these are the only possible two cases, `is_not_equal` is always
         // constrained to 0 or 1.
-        self.cs.enforce_constraint(
-            lc!() + self.variable - other.variable,
-            lc!() + multiplier,
-            is_not_equal.lc(),
-        )?;
-        self.cs.enforce_constraint(
-            lc!() + self.variable - other.variable,
-            (!&is_not_equal).lc(),
-            lc!(),
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable - other.variable,
+                lc!() + multiplier,
+                is_not_equal.lc(),
+            )?;
+            self.cs.enforce_constraint(
+                lc!() + self.variable - other.variable,
+                (!&is_not_equal).lc(),
+                lc!(),
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 2;
+        }
         Ok(is_not_equal)
     }
 
@@ -446,11 +513,16 @@ impl AllocatedFp {
         other: &Self,
         should_enforce: &Boolean<F>,
     ) -> Result<(), SynthesisError> {
-        self.cs.enforce_constraint(
-            lc!() + self.variable - other.variable,
-            lc!() + should_enforce.lc(),
-            lc!(),
-        )
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable - other.variable,
+                lc!() + should_enforce.lc(),
+                lc!(),
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+        Ok(())
     }
 
     /// Enforces that self != other if `should_enforce.is_eq(&Boolean::TRUE)`.
@@ -465,8 +537,9 @@ impl AllocatedFp {
         // The high level logic is as follows:
         // We want to check that self - other != 0. We do this by checking that
         // (self - other).inverse() exists. In more detail, we check the following:
-        // If `should_enforce == true`, then we set `multiplier = (self - other).inverse()`,
-        // and check that (self - other) * multiplier == 1. (i.e., that the inverse exists)
+        // If `should_enforce == true`, then we set `multiplier = (self -
+        // other).inverse()`, and check that (self - other) * multiplier == 1.
+        // (i.e., that the inverse exists)
         //
         // If `should_enforce == false`, then we set `multiplier == 0`, and check that
         // (self - other) * 0 == 0, which is always satisfied.
@@ -478,11 +551,16 @@ impl AllocatedFp {
             }
         })?;
 
-        self.cs.enforce_constraint(
-            lc!() + self.variable - other.variable,
-            lc!() + multiplier.variable,
-            should_enforce.lc(),
-        )?;
+        if self.enable_lc {
+            self.cs.enforce_constraint(
+                lc!() + self.variable - other.variable,
+                lc!() + multiplier.variable,
+                should_enforce.lc(),
+            )?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
+
         Ok(())
     }
 }
@@ -532,14 +610,20 @@ impl ToBitsGadget for AllocatedFp {
         let mut coeff = F::one();
 
         for bit in bits.iter() {
-            lc = &lc + bit.lc() * coeff;
+            if self.enable_lc {
+                lc = &lc + bit.lc() * coeff;
+            }
 
             coeff.double_in_place();
         }
 
-        lc = lc - &self.variable;
+        if self.enable_lc {
+            lc = lc - &self.variable;
 
-        cs.enforce_constraint(lc!(), lc!(), lc)?;
+            cs.enforce_constraint(lc!(), lc!(), lc)?;
+        } else {
+            self.cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(bits)
     }
@@ -594,8 +678,8 @@ impl CondSelectGadget for AllocatedFp {
         false_val: &Self,
     ) -> Result<Self, SynthesisError> {
         match cond {
-            &Boolean::Constant(true) => Ok(true_val.clone()),
-            &Boolean::Constant(false) => Ok(false_val.clone()),
+            Boolean::Constant(true) => Ok(true_val.clone()),
+            Boolean::Constant(false) => Ok(false_val.clone()),
             _ => {
                 let cs = cond.cs();
                 let result = Self::new_witness(cs.clone(), || {
@@ -607,11 +691,15 @@ impl CondSelectGadget for AllocatedFp {
                 // r = c * a + (1  - c) * b
                 // r = b + c * (a - b)
                 // c * (a - b) = r - b
-                cs.enforce_constraint(
-                    cond.lc(),
-                    lc!() + true_val.variable - false_val.variable,
-                    lc!() + result.variable - false_val.variable,
-                )?;
+                if cs.should_construct_matrices() {
+                    cs.enforce_constraint(
+                        cond.lc(),
+                        lc!() + true_val.variable - false_val.variable,
+                        lc!() + result.variable - false_val.variable,
+                    )?;
+                } else {
+                    cs.borrow_mut().unwrap().num_constraints += 1;
+                }
 
                 Ok(result)
             },
@@ -627,18 +715,23 @@ impl TwoBitLookupGadget for AllocatedFp {
     fn two_bit_lookup(b: &[Boolean<F>], c: &[Self::TableConstant]) -> Result<Self, SynthesisError> {
         debug_assert_eq!(b.len(), 2);
         debug_assert_eq!(c.len(), 4);
-        let result = Self::new_witness(b.cs(), || {
+        let cs = b.cs();
+        let result = Self::new_witness(cs.clone(), || {
             let lsb = usize::from(b[0].value()?);
             let msb = usize::from(b[1].value()?);
             let index = lsb + (msb << 1);
             Ok(c[index])
         })?;
         let one = Variable::One;
-        b.cs().enforce_constraint(
-            lc!() + b[1].lc() * (c[3] - &c[2] - &c[1] + &c[0]) + (c[1] - &c[0], one),
-            lc!() + b[0].lc(),
-            lc!() + result.variable - (c[0], one) + b[1].lc() * (c[0] - &c[2]),
-        )?;
+        if cs.should_construct_matrices() {
+            cs.enforce_constraint(
+                lc!() + b[1].lc() * (c[3] - &c[2] - &c[1] + &c[0]) + (c[1] - &c[0], one),
+                lc!() + b[0].lc(),
+                lc!() + result.variable - (c[0], one) + b[1].lc() * (c[0] - &c[2]),
+            )?;
+        } else {
+            cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -655,7 +748,8 @@ impl ThreeBitCondNegLookupGadget for AllocatedFp {
     ) -> Result<Self, SynthesisError> {
         debug_assert_eq!(b.len(), 3);
         debug_assert_eq!(c.len(), 4);
-        let result = Self::new_witness(b.cs(), || {
+        let cs = b.cs();
+        let result = Self::new_witness(cs.clone(), || {
             let lsb = usize::from(b[0].value()?);
             let msb = usize::from(b[1].value()?);
             let index = lsb + (msb << 1);
@@ -670,16 +764,20 @@ impl ThreeBitCondNegLookupGadget for AllocatedFp {
             Ok(y)
         })?;
 
-        let y_lc = b0b1.lc() * (c[3] - &c[2] - &c[1] + &c[0])
-            + b[0].lc() * (c[1] - &c[0])
-            + b[1].lc() * (c[2] - &c[0])
-            + (c[0], Variable::One);
-        // enforce y * (1 - 2 * b_2) == res
-        b.cs().enforce_constraint(
-            y_lc.clone(),
-            b[2].lc() * F::from(2u64).neg() + (F::one(), Variable::One),
-            lc!() + result.variable,
-        )?;
+        if cs.should_construct_matrices() {
+            let y_lc = b0b1.lc() * (c[3] - &c[2] - &c[1] + &c[0])
+                + b[0].lc() * (c[1] - &c[0])
+                + b[1].lc() * (c[2] - &c[0])
+                + (c[0], Variable::One);
+            // enforce y * (1 - 2 * b_2) == res
+            cs.enforce_constraint(
+                y_lc.clone(),
+                b[2].lc() * F::from(2u64).neg() + (F::one(), Variable::One),
+                lc!() + result.variable,
+            )?;
+        } else {
+            cs.borrow_mut().unwrap().num_constraints += 1;
+        }
 
         Ok(result)
     }
@@ -695,7 +793,11 @@ impl AllocVar for AllocatedFp {
         let cs = ns.cs();
         if mode == AllocationMode::Constant {
             let v = *f()?.borrow();
-            let lc = cs.new_lc(lc!() + (v, Variable::One))?;
+            let lc = cs.new_lc(if cs.should_construct_matrices() {
+                lc!() + (v, Variable::One)
+            } else {
+                lc!()
+            })?;
             Ok(Self::new(Some(v), lc, cs))
         } else {
             let mut value = None;