FreeCalypso > hg > ffs-editor

annotate src/libsys/rand.c @ 1:5a26a267684f

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
targets: new minimal headers created
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 15 May 2020 01:45:24 +0000
parents 92470e5d0b9e
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
0
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
1 /*
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
2 * This version of rand() has been lifted from Ancient UNIX, and modified
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
3 * to match the version used in TI's TCS211 GSM firmware, as revealed by
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
4 * disassembly of rand.obj in the rts16le_flash.lib binary library used
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
5 * by that semi-src package. TI's version (most likely from their compiler
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
6 * tools group, rather than the GSM fw group, but who knows) uses the
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
7 * same trivial implementation of rand() as the original Ancient UNIX libc,
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
8 * but with one change: TI's return value is right-shifted by 16 bits
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
9 * compared to what the Ancient UNIX rand() would have returned.
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
10 * The caller thus gets back only 15 pseudo-random bits rather than 31,
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
11 * but then the lower bits of the original rand() return value are
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
12 * known to be pretty bad.
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
13 *
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
14 * rand() is used by some FFS code in reclaim.c. If we don't provide our
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
15 * own version of rand() and let the linker pull the version from newlib,
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
16 * the link fails because the latter uses malloc. This ancient implementation
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
17 * of rand() is quite poor, but my plan is to look into possibly adopting
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
18 * some better PRNG after we get the basic TI GSM firmware reintegrated.
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
19 */
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
20
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
21 static long randx = 1;
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
22
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
23 srand(x)
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
24 unsigned x;
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
25 {
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
26 randx = x;
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
27 }
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
28
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
29 rand()
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
30 {
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
31 return ((randx = randx * 1103515245 + 12345) & 0x7fffffff) >> 16;
92470e5d0b9e src: partial import from FC Selenite
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
32 }