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172 lines
4.0 KiB
172 lines
4.0 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* IEEE754 floating point arithmetic |
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* double precision: common utilities |
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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 "ieee754dp.h" |
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union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y) |
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{ |
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int s; |
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COMPXDP; |
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COMPYDP; |
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EXPLODEXDP; |
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EXPLODEYDP; |
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ieee754_clearcx(); |
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FLUSHXDP; |
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FLUSHYDP; |
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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 ieee754dp_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 ieee754dp_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 ieee754dp_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 ieee754dp_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 ieee754dp_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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DPSIGN(y) ^= 1; |
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return y; |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): |
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DPDNORMX; |
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fallthrough; |
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case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): |
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/* normalize ym,ye */ |
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DPDNORMY; |
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break; |
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case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): |
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/* normalize xm,xe */ |
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DPDNORMX; |
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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 & DP_HIDDEN_BIT); |
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assert(ym & DP_HIDDEN_BIT); |
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/* provide guard,round and stick bit dpace */ |
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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 = XDPSRS(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 = XDPSRS(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 <= DP_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 >> (DP_FBITS + 1 + 3)) { /* carry out */ |
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xm = XDPSRS1(xm); /* shift preserving sticky */ |
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xe++; |
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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 ieee754dp_zero(1); /* round negative inf. => sign = -1 */ |
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else |
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return ieee754dp_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 >> (DP_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 ieee754dp_format(xs, xe, xm); |
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}
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