101 lines
2.7 KiB
C
101 lines
2.7 KiB
C
/*---------------------------------------------------------------------------+
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| reg_u_mul.c |
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| $Id: reg_u_mul.c,v 1.7 2003-10-05 12:26:11 sshwarts Exp $
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| Core multiplication routine |
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| Copyright (C) 1992,1993,1995,1997,1999 |
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| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
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| E-mail billm@melbpc.org.au |
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+---------------------------------------------------------------------------*/
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/*---------------------------------------------------------------------------+
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| Basic multiplication routine. |
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| Does not check the resulting exponent for overflow/underflow |
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| Internal working is at approx 128 bits. |
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| Result is rounded to nearest 53 or 64 bits, using "nearest or even". |
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+---------------------------------------------------------------------------*/
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#include "exception.h"
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#include "fpu_emu.h"
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#include "control_w.h"
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int FPU_u_mul(const FPU_REG *a, const FPU_REG *b, FPU_REG *c, u16 cw,
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u_char sign, int expon)
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{
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u64 mu, ml, mi;
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u32 lh, ll, th, tl;
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#ifdef PARANOID
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if (! (a->sigh & 0x80000000) || ! (b->sigh & 0x80000000))
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{
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INTERNAL(0x205);
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}
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#endif
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ml = a->sigl;
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ml *= b->sigl;
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ll = ml;
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lh = ml >> 32;
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mu = a->sigh;
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mu *= b->sigh;
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mi = a->sigh;
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mi *= b->sigl;
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tl = mi;
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th = mi >> 32;
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lh += tl;
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if (tl > lh)
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mu ++;
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mu += th;
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mi = a->sigl;
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mi *= b->sigh;
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tl = mi;
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th = mi >> 32;
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lh += tl;
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if (tl > lh)
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mu ++;
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mu += th;
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ml = lh;
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ml <<= 32;
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ml += ll;
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expon -= EXP_BIAS-1;
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if (expon <= EXP_WAY_UNDER)
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expon = EXP_WAY_UNDER;
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/* if the addition of signed 16-bit values overflowed, substitute
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the maximum positive exponent to force FPU_round to produce overflow */
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if (expon > 0x7FFE)
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expon = 0x7FFE;
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c->exp = expon;
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if (! (mu & BX_CONST64(0x8000000000000000)))
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{
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mu <<= 1;
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if (ml & BX_CONST64(0x8000000000000000))
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mu |= 1;
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ml <<= 1;
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c->exp --;
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}
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ll = ml;
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lh = ml >> 32;
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if (ll)
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lh |= 1;
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c->sigl = mu;
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c->sigh = mu >> 32;
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return FPU_round(c, lh, cw, sign);
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}
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