On 07/30/2013 08:51 PM, Gregory Warnes wrote: > How about enclosing the bit-for-bit tests in > #ifdef IEEE754_Compliant > ... > #endif
Merely knowing that a platform conforms to IEEE 754 is not sufficient to guarantee bit-for-bit compatibility. The order of operations also matters, and compliers can, and do, re-arrange, eliminate, and combine operations as an optimization. Even if the rounding rules are the same, the cost of various operations or the primitive operations that are available are not the same between platforms, so the optimizations also differ, and also depend on compiler version and build environment. Search http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html for "float" for some idea of the myriad complier options which influence this. Getting bit-for-bit IEEE 754 behavior on some platforms comes at the expense of both speed and precision. For example, on the x87, the FPU registers are 80 bits, and all register instructions operate on the full 80 bits, while IEEE 754 defines no such format (64 bits being the closest). To avoid this requires -ffloat-store, which forces all variables to be stored in RAM, which is a significant performance hit for most programs and makes rounding error worse. I can't see this as being good for gnuradio in any way. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
