http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21718
--- Comment #17 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- I confirm that it is an architecture-dependent bug. I can't reproduce any error with your test program on http://www.exploringbinary.com/incorrectly-rounded-conversions-in-gcc-and-glibc/ even with old gcc versions, from an x86_64 machine. With GCC 4.3.5 (Debian 4.3.5-4) on Debian 6.0.7 (squeeze): 0.500000000000000166533453693773481063544750213623046875 Correct = 0x1.0000000000002p-1 gcc = 0x1.0000000000002p-1 strtod = 0x1.0000000000001p-1 3.518437208883201171875e13 Correct = 0x1.0000000000002p+45 gcc = 0x1.0000000000002p+45 strtod = 0x1.0000000000001p+45 62.5364939768271845828 Correct = 0x1.f44abd5aa7ca4p+5 gcc = 0x1.f44abd5aa7ca4p+5 strtod = 0x1.f44abd5aa7ca3p+5 8.10109172351e-10 Correct = 0x1.bd5cbaef0fd0cp-31 gcc = 0x1.bd5cbaef0fd0cp-31 strtod = 0x1.bd5cbaef0fd0cp-31 1.50000000000000011102230246251565404236316680908203125 Correct = 0x1.8p+0 gcc = 0x1.8p+0 strtod = 0x1.8p+0 9007199254740991.4999999999999999999999999999999995 Correct = 0x1.fffffffffffffp+52 gcc = 0x1.fffffffffffffp+52 strtod = 0x1.fffffffffffffp+52 If I add the -m32 option, I get the same output except: 8.10109172351e-10 Correct = 0x1.bd5cbaef0fd0cp-31 gcc = 0x1.bd5cbaef0fd0cp-31 strtod = 0x1.bd5cbaef0fd0dp-31 and the -mfpmath=387 option doesn't change anything. On a Debian 6.0.7 (squeeze) 32-bit machine, with GCC 4.3.5 (Debian 4.3.5-4) and GCC 4.4.5 (Debian 4.4.5-8): 0.500000000000000166533453693773481063544750213623046875 Correct = 0x1.0000000000002p-1 gcc = 0x1.0000000000001p-1 strtod = 0x1.0000000000001p-1 3.518437208883201171875e13 Correct = 0x1.0000000000002p+45 gcc = 0x1.0000000000002p+45 strtod = 0x1.0000000000001p+45 62.5364939768271845828 Correct = 0x1.f44abd5aa7ca4p+5 gcc = 0x1.f44abd5aa7ca4p+5 strtod = 0x1.f44abd5aa7ca3p+5 8.10109172351e-10 Correct = 0x1.bd5cbaef0fd0cp-31 gcc = 0x1.bd5cbaef0fd0cp-31 strtod = 0x1.bd5cbaef0fd0dp-31 1.50000000000000011102230246251565404236316680908203125 Correct = 0x1.8p+0 gcc = 0x1.8000000000001p+0 strtod = 0x1.8p+0 9007199254740991.4999999999999999999999999999999995 Correct = 0x1.fffffffffffffp+52 gcc = 0x1p+53 strtod = 0x1.fffffffffffffp+52 Since the computations are done at compile time, it is the architecture of the GCC code that matters, not the one of the generated code (so that using -m32 on a 64-bit machine doesn't have any effect on the GCC side).
