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

1 files changed, 160 insertions, 0 deletions

diff --git a/lib/addsf3.c b/lib/addsf3.c
new file mode 100644
index 000000000..e6d132084
--- /dev/null
+++ 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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