186 lines
4.3 KiB
C
186 lines
4.3 KiB
C
/*---------------------------------------------------------------------------+
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| div_Xsig.S |
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| Division subroutine for 96 bit quantities |
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| Copyright (C) 1994,1995,1999 |
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| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, |
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| Australia. E-mail billm@melbpc.org.au |
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+---------------------------------------------------------------------------*/
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/*---------------------------------------------------------------------------+
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| Divide the 96 bit quantity pointed to by a, by that pointed to by b, and |
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| put the 96 bit result at the location d. |
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| The result may not be accurate to 96 bits. It is intended for use where |
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| a result better than 64 bits is required. The result should usually be |
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| good to at least 94 bits. |
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| The returned result is actually divided by one half. This is done to |
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| prevent overflow. |
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| .aaaaaaaaaaaaaa / .bbbbbbbbbbbbb -> .dddddddddddd |
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+---------------------------------------------------------------------------*/
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#include "exception.h"
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#include "fpu_emu.h"
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#include "poly.h"
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void div_Xsig(const Xsig *aa, const Xsig *b, Xsig *dest)
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{
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Xsig a = *aa, xpr, result;
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u32 prodh, prodl, den, wd;
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u64 num, prod;
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#ifdef PARANOID
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if ( (b->msw & 0x80000000) == 0 )
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{
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EXCEPTION(EX_INTERNAL|0x240);
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return;
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}
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#endif
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/* Shift a right */
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a.lsw >>= 1;
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if ( a.midw & 1 )
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a.lsw |= 0x80000000;
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a.midw >>= 1;
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if ( a.msw & 1 )
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a.midw |= 0x80000000;
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a.msw >>= 1;
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num = a.msw;
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num <<= 32;
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num |= a.midw;
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den = b->msw + 1;
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if ( den )
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{
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result.msw = num / den;
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}
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else
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result.msw = a.msw;
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xpr = *b;
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mul32_Xsig(&xpr, result.msw);
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a.msw -= xpr.msw;
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wd = a.midw;
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a.midw -= xpr.midw;
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if ( a.midw > wd )
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a.msw --;
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wd = a.lsw;
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a.lsw -= xpr.lsw;
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if ( a.lsw > wd )
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{
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a.midw --;
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if ( a.midw == 0xffffffff )
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a.msw --;
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}
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#ifdef PARANOID
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if ( a.msw > 1 )
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{
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EXCEPTION(EX_INTERNAL|0x241);
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}
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#endif
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while ( (a.msw != 0) || (a.midw > b->msw) )
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{
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wd = a.midw;
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a.midw -= b->msw;
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if ( a.midw > wd )
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a.msw --;
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wd = a.lsw;
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a.lsw -= b->midw;
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if ( a.lsw > wd )
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{
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a.midw --;
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if ( a.midw == 0xffffffff )
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a.msw --;
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}
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result.msw ++;
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}
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/* Whew! result.msw is now done. */
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num = a.midw;
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num <<= 32;
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num |= a.lsw;
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if ( den )
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{
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result.midw = num / den;
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}
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else
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result.midw = a.midw;
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prod = result.midw;
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prod *= b->msw;
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a.midw -= prod >> 32;
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prodl = prod;
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wd = a.lsw;
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a.lsw -= prodl;
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if ( a.lsw > wd )
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a.midw --;
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prod = result.midw;
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prod *= b->midw;
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prodh = prod >> 32;
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wd = a.lsw;
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a.lsw -= prodh;
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if ( a.lsw > wd )
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a.midw --;
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#ifdef PARANOID
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if ( a.midw > 1 )
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{
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EXCEPTION(EX_INTERNAL|0x242);
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}
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#endif
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while ( (a.midw != 0) || (a.lsw > b->msw) )
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{
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wd = a.lsw;
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a.lsw -= b->msw;
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if ( a.lsw > wd )
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a.midw --;
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result.midw ++;
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}
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/* Now result.msw is done, the lsw is next... */
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num = a.lsw;
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num <<= 32;
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if ( den )
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{
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result.lsw = num / den;
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}
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else
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result.lsw = a.lsw;
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prod = result.lsw;
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prod *= b->msw;
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a.lsw -= prod >> 32;
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#ifdef PARANOID
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if ( a.lsw > 2 )
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{
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EXCEPTION(EX_INTERNAL|0x243);
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}
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#endif
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result.lsw -= a.lsw;
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/* Hey! we're done. */
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*dest = result;
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}
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