Am Tue, 14 May 2013 18:59:14 +0200 schrieb "Iain Buclaw" <ibuc...@ubuntu.com>:
> core.exception.AssertError@libphobos/src/std/conv.d(2524): http://dpaste.dzfl.pl/f995a4f3 Caused by a subtle difference when parsing floating point values in the compiler. ldc produces the same result as gdc. The asm generated for loading the 1.23456E+2 constant value is: dmd: -------- fldt 0x806f5dc #0x400ff120000000000000 fstpt -0x18(%ebp) movw $0x0,-0xe(%ebp) fldt 0x806f5e8 #0x4005f6e978d4fdf3b645 -------- gdc: -------- movabs $0xf6e978d4fdf3b646,%rcx mov $0x4005,%ebx #0x4005f6e978d4fdf3b646 -------- I think rounding at compile time could be the issue. The 1.23456E+2 value cannot be represented exactly with 80bit reals. If I calculate the mantissa manually I get the ...45 if I simply disregard the part of the mantissa which is > 63 bit. If I round after the 63. bit I get the ..46 result. So the question is: Is the rounding mode which should be used when parsing a floating point literal specified? I guess not. Then we could simply use a value in the test which fits completely into the mantissa, like 123.375 (I wonder whether .456 was used cause it fills all bits in the mantissa or whether that was by accident...)
