From e63dab55ec0ea8b99749565e61cdcee25579eb72 Mon Sep 17 00:00:00 2001 From: Tim Peters Date: Tue, 5 Sep 2006 02:00:47 +0000 Subject: [PATCH] Merge rev 51711 from the 2.5 branch. i_divmod(): As discussed on Python-Dev, changed the overflow checking to live happily with recent gcc optimizations that assume signed integer arithmetic never overflows. --- Misc/NEWS | 3 +++ Objects/intobject.c | 10 ++++++++-- 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/Misc/NEWS b/Misc/NEWS index dd8cdf610eab..9427ab232beb 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -12,6 +12,9 @@ What's New in Python 2.4.4c1? Core and builtins ----------------- +- Overflow checking code in integer division ran afoul of new gcc + optimizations. Changed to be more standard-conforming. + - Patch #1541585: fix buffer overrun when performing repr() on a unicode string in a build with wide unicode (UCS-4) support. diff --git a/Objects/intobject.c b/Objects/intobject.c index 763ed53d4b9c..1a7e2f7c8610 100644 --- a/Objects/intobject.c +++ b/Objects/intobject.c @@ -478,8 +478,14 @@ i_divmod(register long x, register long y, "integer division or modulo by zero"); return DIVMOD_ERROR; } - /* (-sys.maxint-1)/-1 is the only overflow case. */ - if (y == -1 && x < 0 && x == -x) + /* (-sys.maxint-1)/-1 is the only overflow case. x is the most + * negative long iff x < 0 and, on a 2's-complement box, x == -x. + * However, -x is undefined (by C) if x /is/ the most negative long + * (it's a signed overflow case), and some compilers care. So we cast + * x to unsigned long first. However, then other compilers warn about + * applying unary minus to an unsigned operand. Hence the weird "0-". + */ + if (y == -1 && x < 0 && (unsigned long)x == 0-(unsigned long)x) return DIVMOD_OVERFLOW; xdivy = x / y; xmody = x - xdivy * y; -- 2.47.3