Adding soft-float comparisons, addition, subtraction, multiplication and negation
git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@107400 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/addsf3.c b/lib/addsf3.c
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+++ b/lib/addsf3.c
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+/*
+ * The LLVM Compiler Infrastructure
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ */
+
+#define SINGLE_PRECISION
+#include "fp_lib.h"
+
+// This file implements single-precision soft-float addition and subtraction
+// with the IEEE-754 default rounding (to nearest, ties to even).
+
+fp_t __addsf3(fp_t a, fp_t b) {
+
+ rep_t aRep = toRep(a);
+ rep_t bRep = toRep(b);
+ const rep_t aAbs = aRep & absMask;
+ const rep_t bAbs = bRep & absMask;
+
+ // Detect if a or b is zero, infinity, or NaN.
+ if (aAbs - 1U >= infRep - 1U || bAbs - 1U >= infRep - 1U) {
+
+ // NaN + anything = qNaN
+ if (aAbs > infRep) return fromRep(toRep(a) | quietBit);
+ // anything + NaN = qNaN
+ if (bAbs > infRep) return fromRep(toRep(b) | quietBit);
+
+ if (aAbs == infRep) {
+ // +/-infinity + -/+infinity = qNaN
+ if ((toRep(a) ^ toRep(b)) == signBit) return fromRep(qnanRep);
+ // +/-infinity + anything remaining = +/- infinity
+ else return a;
+ }
+
+ // anything remaining + +/-infinity = +/-infinity
+ if (bAbs == infRep) return b;
+
+ // zero + anything = anything
+ if (!aAbs) {
+ // but we need to get the sign right for zero + zero
+ if (!bAbs) return fromRep(toRep(a) & toRep(b));
+ else return b;
+ }
+
+ // anything + zero = anything
+ if (!bAbs) return a;
+ }
+
+ // Swap a and b if necessary so that a has the larger absolute value.
+ if (bAbs > aAbs) {
+ const rep_t temp = aRep;
+ aRep = bRep;
+ bRep = temp;
+ }
+
+ // Extract the exponent and significand from the (possibly swapped) a and b.
+ int aExponent = aRep >> significandBits & maxExponent;
+ int bExponent = bRep >> significandBits & maxExponent;
+ rep_t aSignificand = aRep & significandMask;
+ rep_t bSignificand = bRep & significandMask;
+
+ // Normalize any denormals, and adjust the exponent accordingly.
+ if (aExponent == 0) aExponent = normalize(&aSignificand);
+ if (bExponent == 0) bExponent = normalize(&bSignificand);
+
+ // The sign of the result is the sign of the larger operand, a. If they
+ // have opposite signs, we are performing a subtraction; otherwise addition.
+ const rep_t resultSign = aRep & signBit;
+ const bool subtraction = (aRep ^ bRep) & signBit;
+
+ // Shift the significands to give us round, guard and sticky, and or in the
+ // implicit significand bit. (If we fell through from the denormal path it
+ // was already set by normalize( ), but setting it twice won't hurt
+ // anything.)
+ aSignificand = (aSignificand | implicitBit) << 3;
+ bSignificand = (bSignificand | implicitBit) << 3;
+
+ // Shift the significand of b by the difference in exponents, with a sticky
+ // bottom bit to get rounding correct.
+ const int align = aExponent - bExponent;
+ if (align) {
+ if (align < typeWidth) {
+ const bool sticky = bSignificand << (typeWidth - align);
+ bSignificand = bSignificand >> align | sticky;
+ } else {
+ bSignificand = 1; // sticky; b is known to be non-zero.
+ }
+ }
+
+ if (subtraction) {
+ aSignificand -= bSignificand;
+
+ // If a == -b, return +zero.
+ if (aSignificand == 0) return fromRep(0);
+
+ // If partial cancellation occured, we need to left-shift the result
+ // and adjust the exponent:
+ if (aSignificand < implicitBit << 3) {
+ const int shift = rep_clz(aSignificand) - rep_clz(implicitBit << 3);
+ aSignificand <<= shift;
+ aExponent -= shift;
+ }
+ }
+
+ else /* addition */ {
+ aSignificand += bSignificand;
+
+ // If the addition carried up, we need to right-shift the result and
+ // adjust the exponent:
+ if (aSignificand & implicitBit << 4) {
+ const bool sticky = aSignificand & 1;
+ aSignificand = aSignificand >> 1 | sticky;
+ aExponent += 1;
+ }
+ }
+
+ // If we have overflowed the type, return +/- infinity:
+ if (aExponent >= maxExponent) return fromRep(infRep | resultSign);
+
+ if (aExponent <= 0) {
+ // Result is denormal before rounding; the exponent is zero and we
+ // need to shift the significand.
+ const int shift = 1 - aExponent;
+ const bool sticky = aSignificand << (typeWidth - shift);
+ aSignificand = aSignificand >> shift | sticky;
+ aExponent = 0;
+ }
+
+ // Low three bits are round, guard, and sticky.
+ const int roundGuardSticky = aSignificand & 0x7;
+
+ // Shift the significand into place, and mask off the implicit bit.
+ rep_t result = aSignificand >> 3 & significandMask;
+
+ // Insert the exponent and sign.
+ result |= (rep_t)aExponent << significandBits;
+ result |= resultSign;
+
+ // Final rounding. The result may overflow to infinity, but that is the
+ // correct result in that case.
+ if (roundGuardSticky > 0x4) result++;
+ if (roundGuardSticky == 0x4) result += result & 1;
+ return fromRep(result);
+}
+
+// Subtraction; flip the sign bit of b and add.
+fp_t __subsf3(fp_t a, fp_t b) {
+ return __addsf3(a, fromRep(toRep(b) ^ signBit));
+}
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