FreeCalypso > hg > freecalypso-sw

annotate gsm-fw/services/ffs/rand.c @ 992:a7b0b426f9ca

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target-utils: boot ROM UART autodetection revamped The new implementation should work with both the familiar Calypso C035 boot ROM version found in our regular targets as well as the older Calypso F741979B version found on the vintage D-Sample board.
author Mychaela Falconia <falcon@ivan.Harhan.ORG>
date Wed, 30 Dec 2015 21:28:41 +0000
parents 2beb88a3d528
children
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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1 /*
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2 * This version of rand() has been lifted from Ancient UNIX, and modified
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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3 * to match the version used in TI's TCS211 GSM firmware, as revealed by
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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4 * disassembly of rand.obj in the rts16le_flash.lib binary library used
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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5 * by that semi-src package. TI's version (most likely from their compiler
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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6 * tools group, rather than the GSM fw group, but who knows) uses the
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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7 * same trivial implementation of rand() as the original Ancient UNIX libc,
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8 * but with one change: TI's return value is right-shifted by 16 bits
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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9 * compared to what the Ancient UNIX rand() would have returned.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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10 * The caller thus gets back only 15 pseudo-random bits rather than 31,
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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11 * but then the lower bits of the original rand() return value are
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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12 * known to be pretty bad.
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13 *
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14 * rand() is used by some FFS code in reclaim.c. If we don't provide our
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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15 * own version of rand() and let the linker pull the version from newlib,
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16 * the link fails because the latter uses malloc. This ancient implementation
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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17 * of rand() is quite poor, but my plan is to look into possibly adopting
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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18 * some better PRNG after we get the basic TI GSM firmware reintegrated.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
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19 */
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20
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21 static long randx = 1;
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22
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23 srand(x)
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24 unsigned x;
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25 {
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26 randx = x;
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27 }
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28
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29 rand()
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30 {
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31 return ((randx = randx * 1103515245 + 12345) & 0x7fffffff) >> 16;
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32 }