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big.int: fix negative multi-limb shift right adjust crash

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This commit is contained in:
Jacob Young 2025-03-12 22:04:41 -04:00
parent 8e15321c7c
commit aff2be01c9
2 changed files with 13 additions and 10 deletions
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14
lib/std/math/big/int.zig
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@ -1096,7 +1096,7 @@ pub const Mutable = struct {
/// Asserts there is enough memory to fit the result. The upper bound Limb count is
/// `a.limbs.len + (shift / (@sizeOf(Limb) * 8))`.
pub fn shiftLeft(r: *Mutable, a: Const, shift: usize) void {
llshl(r.limbs[0..], a.limbs[0..a.limbs.len], shift);
llshl(r.limbs, a.limbs, shift);
r.normalize(a.limbs.len + (shift / limb_bits) + 1);
r.positive = a.positive;
}
@ -1165,7 +1165,7 @@ pub const Mutable = struct {
// This shift should not be able to overflow, so invoke llshl and normalize manually
// to avoid the extra required limb.
llshl(r.limbs[0..], a.limbs[0..a.limbs.len], shift);
llshl(r.limbs, a.limbs, shift);
r.normalize(a.limbs.len + (shift / limb_bits));
r.positive = a.positive;
}
@ -1202,17 +1202,11 @@ pub const Mutable = struct {
break :nonzero a.limbs[full_limbs_shifted_out] << not_covered != 0;
};
llshr(r.limbs[0..], a.limbs[0..a.limbs.len], shift);
llshr(r.limbs, a.limbs, shift);
r.len = a.limbs.len - full_limbs_shifted_out;
r.positive = a.positive;
if (nonzero_negative_shiftout) {
if (full_limbs_shifted_out > 0) {
r.limbs[a.limbs.len - full_limbs_shifted_out] = 0;
r.len += 1;
}
r.addScalar(r.toConst(), -1);
}
if (nonzero_negative_shiftout) r.addScalar(r.toConst(), -1);
r.normalize(r.len);
}

9
lib/std/math/big/int_test.zig
View file

@ -2191,6 +2191,15 @@ test "shift-right negative" {
a.setSign(true);
try a.shiftRight(&arg7, 4);
try testing.expect(try a.toInt(i16) == -2048);
var arg8_limbs: [1]Limb = undefined;
var arg8: Mutable = .{
.limbs = &arg8_limbs,
.len = undefined,
.positive = undefined,
};
arg8.shiftRight(.{ .limbs = &.{ 1, 1 }, .positive = false }, @bitSizeOf(Limb));
try testing.expect(arg8.toConst().orderAgainstScalar(-2).compare(.eq));
}
test "sat shift-left simple unsigned" {