From ca08655b808aed2e3abeb64cb67d98a79a661dda Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Thu, 9 Dec 2021 11:37:06 -0800 Subject: [PATCH] bpo-46018: Ensure that math.expm1 does not raise on underflow (GH-29997) (cherry picked from commit 3363e1cb05d0d19ed172ea63606d8cb6268747fc) Co-authored-by: Steve Dower --- .../next/Library/2021-12-09-00-44-42.bpo-46018.hkTI7v.rst | 1 + Modules/mathmodule.c | 8 ++++++-- 2 files changed, 7 insertions(+), 2 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2021-12-09-00-44-42.bpo-46018.hkTI7v.rst diff --git a/Misc/NEWS.d/next/Library/2021-12-09-00-44-42.bpo-46018.hkTI7v.rst b/Misc/NEWS.d/next/Library/2021-12-09-00-44-42.bpo-46018.hkTI7v.rst new file mode 100644 index 00000000000..6ff76f58779 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2021-12-09-00-44-42.bpo-46018.hkTI7v.rst @@ -0,0 +1 @@ +Ensure that :func:`math.expm1` does not raise on underflow. diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c index 16da00817b5..4534176adce 100644 --- a/Modules/mathmodule.c +++ b/Modules/mathmodule.c @@ -977,9 +977,13 @@ is_error(double x) * On some platforms (Ubuntu/ia64) it seems that errno can be * set to ERANGE for subnormal results that do *not* underflow * to zero. So to be safe, we'll ignore ERANGE whenever the - * function result is less than one in absolute value. + * function result is less than 1.5 in absolute value. + * + * bpo-46018: Changed to 1.5 to ensure underflows in expm1() + * are correctly detected, since the function may underflow + * toward -1.0 rather than 0.0. */ - if (fabs(x) < 1.0) + if (fabs(x) < 1.5) result = 0; else PyErr_SetString(PyExc_OverflowError,