FreeCalypso > hg > freecalypso-sw
view gsm-fw/services/ffs/rand.c @ 1029:333015c662bc
fc-shell: tch play implemented
author | Mychaela Falconia <falcon@freecalypso.org> |
---|---|
date | Tue, 31 May 2016 01:53:04 +0000 |
parents | 2beb88a3d528 |
children |
line wrap: on
line source
/* * This version of rand() has been lifted from Ancient UNIX, and modified * to match the version used in TI's TCS211 GSM firmware, as revealed by * disassembly of rand.obj in the rts16le_flash.lib binary library used * by that semi-src package. TI's version (most likely from their compiler * tools group, rather than the GSM fw group, but who knows) uses the * same trivial implementation of rand() as the original Ancient UNIX libc, * but with one change: TI's return value is right-shifted by 16 bits * compared to what the Ancient UNIX rand() would have returned. * The caller thus gets back only 15 pseudo-random bits rather than 31, * but then the lower bits of the original rand() return value are * known to be pretty bad. * * rand() is used by some FFS code in reclaim.c. If we don't provide our * own version of rand() and let the linker pull the version from newlib, * the link fails because the latter uses malloc. This ancient implementation * of rand() is quite poor, but my plan is to look into possibly adopting * some better PRNG after we get the basic TI GSM firmware reintegrated. */ static long randx = 1; srand(x) unsigned x; { randx = x; } rand() { return ((randx = randx * 1103515245 + 12345) & 0x7fffffff) >> 16; }