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fix division max value bug
This commit is contained in:
collin
parent
d08364b71b
commit
279c322f2d
@ -118,7 +118,7 @@ macro_rules! test_int {
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// make sure that we can calculate the inverse of each number
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// Leo signed integer division is non-wrapping. Thus attempting to calculate a
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// division result that wraps should be ignored here.
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if a.checked_neg().is_none() || b.checked_neg().is_none() {
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if a.checked_neg().is_none() {
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continue;
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}
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@ -9,7 +9,6 @@ use crate::{
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Int64,
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Int8,
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};
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use snarkos_models::{
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curves::PrimeField,
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gadgets::{
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@ -24,7 +23,7 @@ use snarkos_models::{
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};
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macro_rules! div_int_impl {
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($($gadget:ident)*) => ($(
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($($gadget:ident),*) => ($(
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impl<F: PrimeField> Div<F> for $gadget {
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type ErrorType = SignedIntegerError;
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@ -86,15 +85,52 @@ macro_rules! div_int_impl {
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&allocated_zero,
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)?;
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// if the numerator is 0, return 0
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let self_is_zero = Boolean::Constant(self.eq(&Self::constant(0 as <$gadget as Int>::IntegerType)));
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// if other is the minimum number, the result will be zero or one
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// -128 / -128 = 1
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// x / -128 = 0 fractional result rounds to 0
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let min = Self::constant(<$gadget as Int>::IntegerType::MIN);
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let other_is_min = other.evaluate_equal(
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&mut cs.ns(|| "other_min_check"),
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&min
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)?;
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let self_is_min = self.evaluate_equal(
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&mut cs.ns(|| "self_min_check"),
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&min
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)?;
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let both_min = Boolean::and(
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&mut cs.ns(|| "both_min"),
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&other_is_min,
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&self_is_min
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)?;
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// if other is the minimum, set other to -1 so the calculation will not fail
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let negative_one = allocated_one.neg(&mut cs.ns(|| "allocated_one"))?;
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let a_valid = min.add(&mut cs.ns(||"a_valid"), &allocated_one);
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let a_set = Self::conditionally_select(
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&mut cs.ns(|| "a_set"),
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&self_is_min,
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&a_valid?,
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&self
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)?;
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let b_set = Self::conditionally_select(
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&mut cs.ns(|| "b_set"),
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&other_is_min,
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&negative_one,
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&other
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)?;
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// If the most significant bits of both numbers are equal, the quotient will be positive
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let a_msb = self.bits.last().unwrap();
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let b_msb = other.bits.last().unwrap();
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let a_msb = self.bits.last().unwrap();
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let positive = a_msb.evaluate_equal(cs.ns(|| "compare_msb"), &b_msb)?;
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// Get the absolute value of each number
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let a_comp = self.neg(&mut cs.ns(|| "a_neg"))?;
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let a_comp = a_set.neg(&mut cs.ns(|| "a_neg"))?;
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let a = Self::conditionally_select(
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&mut cs.ns(|| "a_abs"),
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&a_msb,
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@ -102,12 +138,12 @@ macro_rules! div_int_impl {
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&self
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)?;
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let b_comp = other.neg(&mut cs.ns(|| "b_neg"))?;
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let b_comp = b_set.neg(&mut cs.ns(|| "b_neg"))?;
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let b = Self::conditionally_select(
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&mut cs.ns(|| "b_abs"),
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&b_msb,
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&b_comp,
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&other,
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&b_set,
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)?;
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let mut q = zero.clone();
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@ -142,13 +178,11 @@ macro_rules! div_int_impl {
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&b
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)?;
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let sub = r.sub(
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&mut cs.ns(|| format!("subtract_divisor_{}", i)),
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&b
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);
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r = Self::conditionally_select(
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&mut cs.ns(|| format!("subtract_or_same_{}", i)),
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&can_sub,
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@ -182,6 +216,22 @@ macro_rules! div_int_impl {
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&q_neg,
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)?;
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// set to zero if we know result is fractional
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q = Self::conditionally_select(
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&mut cs.ns(|| "fraction"),
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&other_is_min,
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&allocated_zero,
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&q,
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)?;
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// set to one if we know result is division of the minimum number by itself
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q = Self::conditionally_select(
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&mut cs.ns(|| "one_result"),
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&both_min,
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&allocated_one,
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&q,
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)?;
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Ok(Self::conditionally_select(
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&mut cs.ns(|| "self_or_quotient"),
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&self_is_zero,
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@ -193,4 +243,4 @@ macro_rules! div_int_impl {
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)*)
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}
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div_int_impl!(Int8 Int16 Int32 Int64 Int128);
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div_int_impl!(Int8, Int16, Int32, Int64, Int128);
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@ -282,12 +282,16 @@ fn test_int8_div_constants() {
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for _ in 0..1000 {
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let mut cs = TestConstraintSystem::<Fr>::new();
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let a: i8 = rng.gen_range(-127i8, i8::MAX);
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let b: i8 = rng.gen_range(-127i8, i8::MAX);
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let a: i8 = rng.gen();
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let b: i8 = rng.gen();
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if a.checked_neg().is_none() {
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return;
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}
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let expected = match a.checked_div(b) {
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Some(valid) => valid,
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None => continue,
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None => return,
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};
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let a_bit = Int8::constant(a);
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@ -308,12 +312,16 @@ fn test_int8_div() {
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for _ in 0..100 {
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let mut cs = TestConstraintSystem::<Fr>::new();
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let a: i8 = rng.gen_range(-127i8, i8::MAX);
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let b: i8 = rng.gen_range(-127i8, i8::MAX);
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let a: i8 = rng.gen();
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let b: i8 = rng.gen();
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if a.checked_neg().is_none() {
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continue;
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}
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let expected = match a.checked_div(b) {
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Some(valid) => valid,
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None => continue,
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None => return,
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};
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let a_bit = Int8::alloc(cs.ns(|| "a_bit"), || Ok(a)).unwrap();
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