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| author | Jarkko Hietaniemi <jhi@iki.fi> | 2015-01-28 07:23:43 -0500 |
|---|---|---|
| committer | Jarkko Hietaniemi <jhi@iki.fi> | 2015-01-28 07:23:43 -0500 |
| commit | c53cd05fe82f107ce9fb3b4a57e5d5d016ffc1f5 (patch) | |
| tree | 110def974e701a4e611b4f021e043e9d56c39c28 /numeric.c | |
| parent | c1521c2084bc5cbe818891777547f7d3e204146c (diff) | |
| download | perl-c53cd05fe82f107ce9fb3b4a57e5d5d016ffc1f5.tar.gz | |
infnan: even more comment tweaks
Diffstat (limited to 'numeric.c')
| -rw-r--r-- | numeric.c | 18 |
1 files changed, 12 insertions, 6 deletions
@@ -741,17 +741,23 @@ Perl_grok_infnan(pTHX_ const char** sp, const char* send) * a single UV cannot contain all the possible * NaN payload bits. There would need to be * some more generic syntax than "nan($uv)". + * * Issues to keep in mind: * * (1) In most common cases there would * not be an integral number of bytes that * could be set, only a certain number of bits. - * For example for the common NVSIZE == UVSIZE - * there is room for 52 bits in the payload, - * but one bit is commonly reserved for the - * signal/quiet bit, so 51 bits. For the - * x86 80-bit doubles there would be 62 bits, - * and so forth. + * For example for the common case of + * NVSIZE == UVSIZE == 8 there is room for 52 + * bits in the payload, but the most significant + * bit is commonly reserved for the + * signaling/quiet bit, leaving 51 bits. + * Furthermore, the C99 nan() is supposed + * to generate quiet NaNs, so it is doubtful + * whether it should be able to generate + * signaling NaNs. For the x86 80-bit doubles + * (if building a long double Perl) there would + * be 62 bits (s/q bit being the 63rd). * * (2) Endianness of the payload bits. If the * payload is specified as an UV, the low-order |