Mercurial > cpython-lru_cache-weakref
diff Objects/floatobject.c @ 20827:95201153251c legacy-trunk
SF bug #477221: abs and divmod act oddly with -0.0
Try to ensure that divmod(-0.0, 1.0) -> (-0.0, +0.0) across platforms.
It always did on Windows, and still does. It didn't on Linux. Alas,
there's no platform-independent way to write a test case for this.
Bugfix candidate.
| author | Tim Peters <tim.peters@gmail.com> |
|---|---|
| date | Thu, 01 Nov 2001 23:12:27 +0000 |
| parents | 3751366c2f39 |
| children | 14dc693af532 |
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--- a/Objects/floatobject.c Thu Nov 01 21:51:15 2001 +0000 +++ b/Objects/floatobject.c Thu Nov 01 23:12:27 2001 +0000 @@ -464,17 +464,34 @@ it will always be very close to one. */ div = (vx - mod) / wx; - /* note: checking mod*wx < 0 is incorrect -- underflows to - 0 if wx < sqrt(smallest nonzero double) */ - if (mod && ((wx < 0) != (mod < 0))) { - mod += wx; - div -= 1.0; + if (mod) { + /* ensure the remainder has the same sign as the denominator */ + if ((wx < 0) != (mod < 0)) { + mod += wx; + div -= 1.0; + } + } + else { + /* the remainder is zero, and in the presence of signed zeroes + fmod returns different results across platforms; ensure + it has the same sign as the denominator; we'd like to do + "mod = wx * 0.0", but that may get optimized away */ + mod = 0.0; + if (wx < 0.0) + mod = -mod; } /* snap quotient to nearest integral value */ - floordiv = floor(div); - if (div - floordiv > 0.5) - floordiv += 1.0; - PyFPE_END_PROTECT(div) + if (div) { + floordiv = floor(div); + if (div - floordiv > 0.5) + floordiv += 1.0; + } + else { + /* div is zero - get the same sign as the true quotient */ + div *= div; /* hide "div = +0" from optimizers */ + floordiv = div * vx / wx; /* zero w/ sign of vx/wx */ + } + PyFPE_END_PROTECT(floordiv) return Py_BuildValue("(dd)", floordiv, mod); }
