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std/math/pow: Fix #18553, isOddInteger: Return false if float value is greater than 1 << 53 (see comment), add test cases

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hdert 2024-01-20 03:25:03 +13:00 committed by Andrew Kelley
parent 480a2f7f02
commit 314533c28b
1 changed files with 16 additions and 0 deletions
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16
lib/std/math/pow.zig
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@ -178,10 +178,26 @@ pub fn pow(comptime T: type, x: T, y: T) T {
}
fn isOddInteger(x: f64) bool {
if (@abs(x) >= 1 << 53) {
// From https://golang.org/src/math/pow.go
// 1 << 53 is the largest exact integer in the float64 format.
// Any number outside this range will be truncated before the decimal point and therefore will always be
// an even integer.
// Without this check and if x overflows i64 the @intFromFloat(r.ipart) conversion below will panic
return false;
}
const r = math.modf(x);
return r.fpart == 0.0 and @as(i64, @intFromFloat(r.ipart)) & 1 == 1;
}
test "math.pow.isOddInteger" {
try expect(isOddInteger(math.maxInt(i64) * 2) == false);
try expect(isOddInteger(math.maxInt(i64) * 2 + 1) == false);
try expect(isOddInteger(1 << 53) == false);
try expect(isOddInteger(12.0) == false);
try expect(isOddInteger(15.0) == true);
}
test "math.pow" {
const epsilon = 0.000001;