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BUG: Fix signed overflow issue in npy_gcd for INT_MIN on s390x (#31360) by charris · Pull Request #31379 · numpy/numpy · GitHub

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BUG: Fix signed overflow issue in npy_gcd for INT_MIN on s390x (#31360) #31379

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Merged
charris merged 1 commit into from
May 4, 2026
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BUG: Fix signed overflow issue in npy_gcd for INT_MIN on s390x (#31360) #31379

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11 changes: 10 additions & 1 deletion numpy/_core/src/npymath/npy_math_internal.h.src
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Original file line number Diff line number Diff line change
Expand Up @@ -650,12 +650,21 @@ npy_lcm@c@(@type@ a, @type@ b)
*
* #type = (npy_int, npy_long, npy_longlong)*2#
* #c = (,l,ll)*2#
* #utype = (npy_uint, npy_ulong, npy_ulonglong)*2#
* #func=gcd*3,lcm*3#
*/
NPY_INPLACE @type@
npy_@func@@c@(@type@ a, @type@ b)
{
return npy_@func@u@c@(a < 0 ? -a : a, b < 0 ? -b : b);
/*
* Cast to unsigned to avoid overflow when negating minimum signed value.
* For negative values, cast to unsigned first, then apply negation in
* unsigned arithmetic to avoid undefined behavior.
* This ensures correct behavior across all architectures. #31359
*/
@utype@ a_abs = a < 0 ? (@utype@)(0) - (@utype@)a : (@utype@)a;
@utype@ b_abs = b < 0 ? (@utype@)(0) - (@utype@)b : (@utype@)b;
return (@type@)npy_@func@u@c@(a_abs, b_abs);
}
/**end repeat**/

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12 changes: 8 additions & 4 deletions numpy/_core/tests/test_umath.py
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Expand Up @@ -4160,13 +4160,17 @@ def test_lcm_overflow(self):
assert_equal(np.lcm(a, b), 10 * big)

def test_gcd_overflow(self):
for dtype in (np.int32, np.int64):
# verify that we don't overflow when taking abs(x)
# not relevant for lcm, where the result is unrepresentable anyway
a = dtype(np.iinfo(dtype).min) # negative power of two
# verify that we don't overflow when taking abs(x) for INT_MIN
# this was undefined behavior that manifested on s390x with GCC 11.5
for dtype in (np.int8, np.int16, np.int32, np.int64):
a = dtype(np.iinfo(dtype).min) # INT_MIN
q = -(a // 4)
# Test with INT_MIN as first argument
assert_equal(np.gcd(a, q * 3), q)
assert_equal(np.gcd(a, -q * 3), q)
# Test with INT_MIN as second argument
assert_equal(np.gcd(q * 3, a), q)
assert_equal(np.gcd(-q * 3, a), q)

def test_decimal(self):
from decimal import Decimal
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