feat: Implement hints on field_arithmetic lib (Part 2)

CHANGELOG.md

@@ -2,6 +2,42 @@
 
 #### Upcoming Changes
 
+* Implement hints on field_arithmetic lib (Part 2) [#1004](https://github.com/lambdaclass/cairo-rs/pull/1004)
+
+    `BuiltinHintProcessor` now supports the following hint:
+
+    ```python
+    %{
+        from starkware.python.math_utils import div_mod
+
+        def split(num: int, num_bits_shift: int, length: int):
+            a = []
+            for _ in range(length):
+                a.append( num & ((1 << num_bits_shift) - 1) )
+                num = num >> num_bits_shift
+            return tuple(a)
+
+        def pack(z, num_bits_shift: int) -> int:
+            limbs = (z.d0, z.d1, z.d2)
+            return sum(limb << (num_bits_shift * i) for i, limb in enumerate(limbs))
+
+        a = pack(ids.a, num_bits_shift = 128)
+        b = pack(ids.b, num_bits_shift = 128)
+        p = pack(ids.p, num_bits_shift = 128)
+        # For python3.8 and above the modular inverse can be computed as follows:
+        # b_inverse_mod_p = pow(b, -1, p)
+        # Instead we use the python3.7-friendly function div_mod from starkware.python.math_utils
+        b_inverse_mod_p = div_mod(1, b, p)
+
+
+        b_inverse_mod_p_split = split(b_inverse_mod_p, num_bits_shift=128, length=3)
+
+        ids.b_inverse_mod_p.d0 = b_inverse_mod_p_split[0]
+        ids.b_inverse_mod_p.d1 = b_inverse_mod_p_split[1]
+        ids.b_inverse_mod_p.d2 = b_inverse_mod_p_split[2]
+    %}
+    ```
+
 * Optimizations for hash builtin [#1029](https://github.com/lambdaclass/cairo-rs/pull/1029):
   * Track the verified addresses by offset in a `Vec<bool>` rather than storing the address in a `Vec<Relocatable>`
 

cairo_programs/field_arithmetic.cairo

@@ -124,9 +124,51 @@ namespace field_arithmetic {
         }
     }
 
+    // Computes a * b^{-1} modulo p
+    // NOTE: The modular inverse of b modulo p is computed in a hint and verified outside the hint with a multiplicaiton
+    func div{range_check_ptr}(a: Uint384, b: Uint384, p: Uint384) -> (res: Uint384) {
+        alloc_locals;
+        local b_inverse_mod_p: Uint384;
+        %{
+            from starkware.python.math_utils import div_mod
+
+            def split(num: int, num_bits_shift: int, length: int):
+                a = []
+                for _ in range(length):
+                    a.append( num & ((1 << num_bits_shift) - 1) )
+                    num = num >> num_bits_shift
+                return tuple(a)
+
+            def pack(z, num_bits_shift: int) -> int:
+                limbs = (z.d0, z.d1, z.d2)
+                return sum(limb << (num_bits_shift * i) for i, limb in enumerate(limbs))
+
+            a = pack(ids.a, num_bits_shift = 128)
+            b = pack(ids.b, num_bits_shift = 128)
+            p = pack(ids.p, num_bits_shift = 128)
+            # For python3.8 and above the modular inverse can be computed as follows:
+            # b_inverse_mod_p = pow(b, -1, p)
+            # Instead we use the python3.7-friendly function div_mod from starkware.python.math_utils
+            b_inverse_mod_p = div_mod(1, b, p)
+
+
+            b_inverse_mod_p_split = split(b_inverse_mod_p, num_bits_shift=128, length=3)
+
+            ids.b_inverse_mod_p.d0 = b_inverse_mod_p_split[0]
+            ids.b_inverse_mod_p.d1 = b_inverse_mod_p_split[1]
+            ids.b_inverse_mod_p.d2 = b_inverse_mod_p_split[2]
+        %}
+	uint384_lib.check(b_inverse_mod_p);
+        let (b_times_b_inverse) = mul(b, b_inverse_mod_p, p);
+        assert b_times_b_inverse = Uint384(1, 0, 0);
+
+        let (res: Uint384) = mul(a, b_inverse_mod_p, p);
+        return (res,);
+    }
 }
 
 func test_field_arithmetics_extension_operations{range_check_ptr, bitwise_ptr: BitwiseBuiltin*}() {
+    alloc_locals;
     // Test get_square
 
     //Small prime
@@ -162,6 +204,25 @@ func test_field_arithmetics_extension_operations{range_check_ptr, bitwise_ptr: B
     assert r_c.d1 = 0;
     assert r_c.d2 = 0;
 
+    // Test div
+    // Small inputs
+    let a = Uint384(25, 0, 0);
+    let a_div = Uint384(5, 0, 0);
+    let a_p = Uint384(31, 0, 0);
+    let (a_r) = field_arithmetic.div(a, a_div, a_p);
+    assert a_r.d0 = 5;
+    assert a_r.d1 = 0;
+    assert a_r.d2 = 0;
+
+    // Cairo Prime
+    let b = Uint384(1, 0, 5044639098474805171426);
+    let b_div = Uint384(1, 0, 2);
+    let b_p = Uint384(1, 0, 604462909807314605178880);
+    let (b_r) = field_arithmetic.div(b, b_div, b_p);
+    assert b_r.d0 = 280171807489444591652763463227596156607;
+    assert b_r.d1 = 122028556426724038784654414222572127555;
+    assert b_r.d2 = 410614585309032623322981;
+
     return ();
 }
 

src/hint_processor/builtin_hint_processor/builtin_hint_processor_definition.rs

@@ -84,6 +84,7 @@ use felt::Felt252;
 #[cfg(feature = "skip_next_instruction_hint")]
 use crate::hint_processor::builtin_hint_processor::skip_next_instruction::skip_next_instruction;
 
+use super::field_arithmetic::uint384_div;
 use super::vrf::inv_mod_p_uint512::inv_mod_p_uint512;
 
 pub struct HintProcessorData {
@@ -562,6 +563,7 @@ impl HintProcessor for BuiltinHintProcessor {
             hint_code::UINT384_SIGNED_NN => {
                 uint384_signed_nn(vm, &hint_data.ids_data, &hint_data.ap_tracking)
             }
+            hint_code::UINT384_DIV => uint384_div(vm, &hint_data.ids_data, &hint_data.ap_tracking),
             hint_code::UINT256_MUL_DIV_MOD => {
                 uint256_mul_div_mod(vm, &hint_data.ids_data, &hint_data.ap_tracking)
             }

src/hint_processor/builtin_hint_processor/field_arithmetic.rs

@@ -1,10 +1,12 @@
 use felt::Felt252;
-use num_bigint::BigUint;
+use num_bigint::{BigUint, ToBigInt};
+use num_integer::Integer;
 use num_traits::Zero;
 
-use crate::math_utils::{is_quad_residue, sqrt_prime_power};
+use crate::math_utils::{is_quad_residue, mul_inv, sqrt_prime_power};
 use crate::serde::deserialize_program::ApTracking;
 use crate::stdlib::{collections::HashMap, prelude::*};
+use crate::types::errors::math_errors::MathError;
 use crate::vm::errors::hint_errors::HintError;
 use crate::{
     hint_processor::hint_processor_definition::HintReference, vm::vm_core::VirtualMachine,
@@ -112,6 +114,68 @@
 
     Ok(())
 }
+
+/* Implements Hint:
+ %{
+    from starkware.python.math_utils import div_mod
+
+    def split(num: int, num_bits_shift: int, length: int):
+        a = []
+        for _ in range(length):
+            a.append( num & ((1 << num_bits_shift) - 1) )
+            num = num >> num_bits_shift
+        return tuple(a)
+
+    def pack(z, num_bits_shift: int) -> int:
+        limbs = (z.d0, z.d1, z.d2)
+        return sum(limb << (num_bits_shift * i) for i, limb in enumerate(limbs))
+
+    a = pack(ids.a, num_bits_shift = 128)
+    b = pack(ids.b, num_bits_shift = 128)
+    p = pack(ids.p, num_bits_shift = 128)
+    # For python3.8 and above the modular inverse can be computed as follows:
+    # b_inverse_mod_p = pow(b, -1, p)
+    # Instead we use the python3.7-friendly function div_mod from starkware.python.math_utils
+    b_inverse_mod_p = div_mod(1, b, p)
+
+
+    b_inverse_mod_p_split = split(b_inverse_mod_p, num_bits_shift=128, length=3)
+
+    ids.b_inverse_mod_p.d0 = b_inverse_mod_p_split[0]
+    ids.b_inverse_mod_p.d1 = b_inverse_mod_p_split[1]
+    ids.b_inverse_mod_p.d2 = b_inverse_mod_p_split[2]
+%}
+ */
+pub fn uint384_div(
+    vm: &mut VirtualMachine,
+    ids_data: &HashMap<String, HintReference>,
+    ap_tracking: &ApTracking,
+) -> Result<(), HintError> {
+    // Note: ids.a is not used here, nor is it used by following hints, so we dont need to extract it.
+    let b = pack(BigInt3::from_var_name("b", vm, ids_data, ap_tracking)?, 128)
+        .to_bigint()
+        .unwrap_or_default();
+    let p = pack(BigInt3::from_var_name("p", vm, ids_data, ap_tracking)?, 128)
+        .to_bigint()
+        .unwrap_or_default();
+    let b_inverse_mod_p_addr =
+        get_relocatable_from_var_name("b_inverse_mod_p", vm, ids_data, ap_tracking)?;
+    if b.is_zero() {
+        return Err(MathError::DividedByZero.into());
+    }
+    let b_inverse_mod_p = mul_inv(&b, &p)
+        .mod_floor(&p)
+        .to_biguint()
+        .unwrap_or_default();
+    let b_inverse_mod_p_split = split::<3>(&b_inverse_mod_p, 128);
+    for (i, b_inverse_mod_p_split) in b_inverse_mod_p_split.iter().enumerate() {
+        vm.insert_value(
+            (b_inverse_mod_p_addr + i)?,
+            Felt252::from(b_inverse_mod_p_split),
+        )?;
+    }
+    Ok(())
+}
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -268,4 +332,104 @@
             ((1, 15), 0)
         ];
     }
+
+    #[test]
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+    fn run_uint384_div_ok() {
+        let mut vm = vm_with_range_check!();
+        //Initialize fp
+        vm.run_context.fp = 11;
+        //Create hint_data
+        let ids_data =
+            non_continuous_ids_data![("a", -11), ("b", -8), ("p", -5), ("b_inverse_mod_p", -2)];
+        //Insert ids into memory
+        vm.segments = segments![
+            //a
+            ((1, 0), 25),
+            ((1, 1), 0),
+            ((1, 2), 0),
+            //b
+            ((1, 3), 5),
+            ((1, 4), 0),
+            ((1, 5), 0),
+            //p
+            ((1, 6), 31),
+            ((1, 7), 0),
+            ((1, 8), 0)
+        ];
+        //Execute the hint
+        assert_matches!(run_hint!(vm, ids_data, hint_code::UINT384_DIV), Ok(()));
+        //Check hint memory inserts
+        check_memory![
+            vm.segments.memory,
+            // b_inverse_mod_p
+            ((1, 9), 25),
+            ((1, 10), 0),
+            ((1, 11), 0)
+        ];
+    }
+
+    #[test]
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+    fn run_uint384_div_b_is_zero() {
+        let mut vm = vm_with_range_check!();
+        //Initialize fp
+        vm.run_context.fp = 11;
+        //Create hint_data
+        let ids_data =
+            non_continuous_ids_data![("a", -11), ("b", -8), ("p", -5), ("b_inverse_mod_p", -2)];
+        //Insert ids into memory
+        vm.segments = segments![
+            //a
+            ((1, 0), 25),
+            ((1, 1), 0),
+            ((1, 2), 0),
+            //b
+            ((1, 3), 0),
+            ((1, 4), 0),
+            ((1, 5), 0),
+            //p
+            ((1, 6), 31),
+            ((1, 7), 0),
+            ((1, 8), 0)
+        ];
+        //Execute the hint
+        assert_matches!(
+            run_hint!(vm, ids_data, hint_code::UINT384_DIV),
+            Err(HintError::Math(MathError::DividedByZero))
+        );
+    }
+
+    #[test]
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+    fn run_uint384_div_inconsistent_memory() {
+        let mut vm = vm_with_range_check!();
+        //Initialize fp
+        vm.run_context.fp = 11;
+        //Create hint_data
+        let ids_data =
+            non_continuous_ids_data![("a", -11), ("b", -8), ("p", -5), ("b_inverse_mod_p", -2)];
+        //Insert ids into memory
+        vm.segments = segments![
+            //a
+            ((1, 0), 25),
+            ((1, 1), 0),
+            ((1, 2), 0),
+            //b
+            ((1, 3), 5),
+            ((1, 4), 0),
+            ((1, 5), 0),
+            //p
+            ((1, 6), 31),
+            ((1, 7), 0),
+            ((1, 8), 0),
+            //b_inverse_mod_p
+            ((1, 9), 0)
+        ];
+        //Execute the hint
+        assert_matches!(
+            run_hint!(vm, ids_data, hint_code::UINT384_DIV),
+            Err(HintError::Memory(MemoryError::InconsistentMemory(_, _, _)))
+        );
+    }
 }

src/hint_processor/builtin_hint_processor/hint_code.rs

@@ -749,7 +749,7 @@ s = pack(ids.s, PRIME) % N
 value = res = div_mod(x, s, N)";
 pub(crate) const XS_SAFE_DIV: &str = "value = k = safe_div(res * s - x, N)";
 
-// The following hints support the lib https://github.com/NethermindEth/research-basic-Cairo-operations-big-integers/blob/main/lib/uint384.cairo
+// The following hints support the lib https://github.com/NethermindEth/research-basic-Cairo-operations-big-integers/blob/main/lib
 pub const UINT384_UNSIGNED_DIV_REM: &str = "def split(num: int, num_bits_shift: int, length: int):
     a = []
     for _ in range(length):
@@ -914,6 +914,33 @@ ids.sqrt_x.d2 = split_root_x[2]
 ids.sqrt_gx.d0 = split_root_gx[0]
 ids.sqrt_gx.d1 = split_root_gx[1]
 ids.sqrt_gx.d2 = split_root_gx[2]";
+pub const UINT384_DIV: &str = "from starkware.python.math_utils import div_mod
+
+def split(num: int, num_bits_shift: int, length: int):
+    a = []
+    for _ in range(length):
+        a.append( num & ((1 << num_bits_shift) - 1) )
+        num = num >> num_bits_shift
+    return tuple(a)
+
+def pack(z, num_bits_shift: int) -> int:
+    limbs = (z.d0, z.d1, z.d2)
+    return sum(limb << (num_bits_shift * i) for i, limb in enumerate(limbs))
+
+a = pack(ids.a, num_bits_shift = 128)
+b = pack(ids.b, num_bits_shift = 128)
+p = pack(ids.p, num_bits_shift = 128)
+# For python3.8 and above the modular inverse can be computed as follows:
+# b_inverse_mod_p = pow(b, -1, p)
+# Instead we use the python3.7-friendly function div_mod from starkware.python.math_utils
+b_inverse_mod_p = div_mod(1, b, p)
+
+
+b_inverse_mod_p_split = split(b_inverse_mod_p, num_bits_shift=128, length=3)
+
+ids.b_inverse_mod_p.d0 = b_inverse_mod_p_split[0]
+ids.b_inverse_mod_p.d1 = b_inverse_mod_p_split[1]
+ids.b_inverse_mod_p.d2 = b_inverse_mod_p_split[2]";
 pub const HI_MAX_BITLEN: &str =
     "ids.len_hi = max(ids.scalar_u.d2.bit_length(), ids.scalar_v.d2.bit_length())-1";
 

src/math_utils.rs

@@ -83,7 +83,7 @@ pub fn safe_div_usize(x: usize, y: usize) -> Result<usize, MathError> {
 }
 
 ///Returns num_a^-1 mod p
-fn mul_inv(num_a: &BigInt, p: &BigInt) -> BigInt {
+pub(crate) fn mul_inv(num_a: &BigInt, p: &BigInt) -> BigInt {
     if num_a.is_zero() {
         return BigInt::zero();
     }

src/tests/cairo_run_test.rs

@@ -712,7 +712,7 @@ fn uint384_extension() {
 #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
 fn field_arithmetic() {
     let program_data = include_bytes!("../../cairo_programs/field_arithmetic.json");
-    run_program_simple_with_memory_holes(program_data.as_slice(), 192);
+    run_program_simple_with_memory_holes(program_data.as_slice(), 272);
 }
 
 #[test]