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mul_high: fix aliasing bug when dest overlaps input

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mlgudi
2026-03-15 02:47:26 +00:00
parent 84b38810f1
commit 76da2c3233
1 changed files with 14 additions and 5 deletions
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19
core/math/big/private.odin
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@@ -439,8 +439,14 @@ _private_int_mul_high :: proc(dest, a, b: ^Int, digits: int, allocator := contex
return _private_int_mul_high_comba(dest, a, b, digits)
}
internal_grow(dest, a.used + b.used + 1) or_return
dest.used = a.used + b.used + 1
/*
Set up temporary output `Int`, which we'll swap for `dest` when done.
*/
t := &Int{}
internal_grow(t, a.used + b.used + 1) or_return
t.used = a.used + b.used + 1
pa := a.used
pb := b.used
@@ -451,20 +457,23 @@ _private_int_mul_high :: proc(dest, a, b: ^Int, digits: int, allocator := contex
/*
Calculate the double precision result.
*/
r := _WORD(dest.digit[ix + iy]) + _WORD(a.digit[ix]) * _WORD(b.digit[iy]) + _WORD(carry)
r := _WORD(t.digit[ix + iy]) + _WORD(a.digit[ix]) * _WORD(b.digit[iy]) + _WORD(carry)
/*
Get the lower part.
*/
dest.digit[ix + iy] = DIGIT(r & _WORD(_MASK))
t.digit[ix + iy] = DIGIT(r & _WORD(_MASK))
/*
Carry the carry.
*/
carry = DIGIT(r >> _WORD(_DIGIT_BITS))
}
dest.digit[ix + pb] = carry
t.digit[ix + pb] = carry
}
internal_swap(dest, t)
internal_destroy(t)
return internal_clamp(dest)
}