Author: tg
Revision Date: 2021-07-28 04:07:54 UTC

get the lowest negative number w/o triggering UB, try n…

I have a feeling we’ll need this RSN:

/*
 * styp sv = (uv > 0x7FFFFFFF) ? (styp)(-(styp)(~uv & 0x7FFFFFFF) - 1) : ((styp)uv);
 * utyp uv = (sv < 0) ? ((utyp)(~(utyp)(-(sv + 1)) & 0xFFFFFFFFU)) : ((utyp)sv);
 *
 * long sl = (ul > (ulng)LONG_MAX) ? (long)(-(long)(~ul) - 1L) : ((long)ul);
 * ulng ul = (sl < 0) ? ((ulng)(~(ulng)(-(sl + 1L)))) : ((ulng)ul);
 *
 * styp sneg = (uval > 0) ? (styp)(-(styp)((uval - 1U) & 0x7FFFFFFF) - 1) : (styp)0;
 */

The first twice two are what I figured out how to convert between
internal two’s complement and ISO C’s signed integer types, once
for mksh’s 32-bit arithmetics, once for POSIX’ C long arithmetics
(both implemented, as already announced, on standard integer type
(probably just long for both checking it’s wide enough), as fixed
width types have lower conversion rank). The last negates from an
unsigned 0‥-TYPE_MIN to a signed TYPE_MIN‥0 and is what this com‐
mit introduced in actual prod code.

This rabbit hole is a bottomless barrel… I still want my Ͻ…

Author: tg
Revision Date: 2017-07-26 23:02:23 UTC

make readonly idempotent; spotted by selk from Dragora