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168 lines
3.9 KiB
168 lines
3.9 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* IEEE754 floating point arithmetic |
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* single precision |
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*/ |
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/* |
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* MIPS floating point support |
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* Copyright (C) 1994-2000 Algorithmics Ltd. |
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*/ |
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#include "ieee754sp.h" |
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union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y) |
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{ |
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int s; |
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COMPXSP; |
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COMPYSP; |
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EXPLODEXSP; |
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EXPLODEYSP; |
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ieee754_clearcx(); |
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FLUSHXSP; |
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FLUSHYSP; |
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switch (CLPAIR(xc, yc)) { |
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case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN): |
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case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN): |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN): |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN): |
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case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN): |
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return ieee754sp_nanxcpt(y); |
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case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN): |
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case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN): |
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case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO): |
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case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM): |
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case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM): |
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case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF): |
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return ieee754sp_nanxcpt(x); |
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case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN): |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN): |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN): |
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case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN): |
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return y; |
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case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN): |
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case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO): |
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case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM): |
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case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM): |
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case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF): |
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return x; |
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/* |
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* Infinity handling |
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*/ |
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case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF): |
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if (xs != ys) |
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return x; |
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ieee754_setcx(IEEE754_INVALID_OPERATION); |
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return ieee754sp_indef(); |
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case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF): |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF): |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF): |
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return ieee754sp_inf(ys ^ 1); |
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case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO): |
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case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM): |
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case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM): |
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return x; |
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/* |
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* Zero handling |
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*/ |
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case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO): |
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if (xs != ys) |
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return x; |
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else |
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return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD); |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO): |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO): |
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return x; |
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case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM): |
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case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM): |
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/* quick fix up */ |
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SPSIGN(y) ^= 1; |
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return y; |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): |
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SPDNORMX; |
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fallthrough; |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): |
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SPDNORMY; |
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break; |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): |
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SPDNORMX; |
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break; |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): |
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break; |
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} |
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/* flip sign of y and handle as add */ |
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ys ^= 1; |
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assert(xm & SP_HIDDEN_BIT); |
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assert(ym & SP_HIDDEN_BIT); |
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/* provide guard,round and stick bit space */ |
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xm <<= 3; |
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ym <<= 3; |
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if (xe > ye) { |
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/* |
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* have to shift y fraction right to align |
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*/ |
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s = xe - ye; |
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ym = XSPSRS(ym, s); |
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ye += s; |
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} else if (ye > xe) { |
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/* |
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* have to shift x fraction right to align |
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*/ |
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s = ye - xe; |
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xm = XSPSRS(xm, s); |
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xe += s; |
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} |
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assert(xe == ye); |
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assert(xe <= SP_EMAX); |
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if (xs == ys) { |
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/* generate 28 bit result of adding two 27 bit numbers |
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*/ |
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xm = xm + ym; |
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if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */ |
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SPXSRSX1(); /* shift preserving sticky */ |
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} |
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} else { |
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if (xm >= ym) { |
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xm = xm - ym; |
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} else { |
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xm = ym - xm; |
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xs = ys; |
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} |
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if (xm == 0) { |
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if (ieee754_csr.rm == FPU_CSR_RD) |
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return ieee754sp_zero(1); /* round negative inf. => sign = -1 */ |
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else |
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return ieee754sp_zero(0); /* other round modes => sign = 1 */ |
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} |
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/* normalize to rounding precision |
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*/ |
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while ((xm >> (SP_FBITS + 3)) == 0) { |
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xm <<= 1; |
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xe--; |
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} |
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} |
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return ieee754sp_format(xs, xe, xm); |
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}
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