On Wed, Jan 05, 2011 at 06:09:34PM +0100, Alexander Graf wrote: > > On 02.01.2011, at 15:39, Aurelien Jarno wrote: > > > On PPC the default qNaN doesn't have the sign bit set. > > The spec says "don't care" for the sign bit. Did you extract the value > empirically? I'm not saying it's wrong - the default 32 Bit value seems to be > 0x7FC0_0000 (2.06 ISA 6.6.2.2).
"don't care" is for detecting a qNaN which can be represented by thousands of different values. It's different from the default qNaN. 2.06 ISA 6.6.2.2 is for vector operations, which are always 32-bit. We are also using this value, this time through softfloat-specialize.h (look at float32_default_nan). For 64-bit values, the default value is defined in 4.3. For the long term, we should remove the default qNaN value from target-ppc/op_helper.c and only use the one in softfloat-specialize.h. However it needs reworking of part of the softfloat library first. > Hrm ... reading section 5.4.2: > > A special QNaN is sometimes supplied as the default QNaN for a disabled > invalid-operation exception; it has a plus sign, the leftmost 6 bits of the > combination field set to 0b111110 and remaining bits in the combination field > and the trailing significand field set to zero. > That's for decimal floating point, and not binary floating point, however it seems they use the same convention. Thanks for the review. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurel...@aurel32.net http://www.aurel32.net
