1 files changed, 135 insertions, 0 deletions
diff --git a/lib/muldf3.c b/lib/muldf3.c
new file mode 100644
index 000000000..77e9ed19c
--- /dev/null
+++ b/lib/muldf3.c
@@ -0,0 +1,135 @@
+/*
+ *                     The LLVM Compiler Infrastructure
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ */
+
+#define DOUBLE_PRECISION
+#include "fp_lib.h"
+
+// This file implements double-precision soft-float multiplication with the
+// IEEE-754 default rounding (to nearest, ties to even).
+
+#define loWord(a) (a & 0xffffffffU)
+#define hiWord(a) (a >> 32)
+
+// 64x64 -> 128 wide multiply for platforms that don't have such an operation;
+// some 64-bit platforms have this operation, but they tend to have hardware
+// floating-point, so we don't bother with a special case for them here.
+static inline void wideMultiply(rep_t a, rep_t b, rep_t *hi, rep_t *lo) {
+    // Each of the component 32x32 -> 64 products
+    const uint64_t plolo = loWord(a) * loWord(b);
+    const uint64_t plohi = loWord(a) * hiWord(b);
+    const uint64_t philo = hiWord(a) * loWord(b);
+    const uint64_t phihi = hiWord(a) * hiWord(b);
+    // Sum terms that compute to lo in a way that allows us to get the carry
+    const uint64_t r0 = loWord(plolo);
+    const uint64_t r1 = hiWord(plolo) + loWord(plohi) + loWord(philo);
+    *lo = r0 + (r1 << 32);
+    // Sum terms contributing to hi with the carry from lo
+    *hi = hiWord(plohi) + hiWord(philo) + hiWord(r1) + phihi;
+}
+
+fp_t __muldf3(fp_t a, fp_t b) {
+    
+    const unsigned int aExponent = toRep(a) >> significandBits & maxExponent;
+    const unsigned int bExponent = toRep(b) >> significandBits & maxExponent;
+    const rep_t productSign = (toRep(a) ^ toRep(b)) & signBit;
+    
+    rep_t aSignificand = toRep(a) & significandMask;
+    rep_t bSignificand = toRep(b) & significandMask;
+    int scale = 0;
+    
+    // Detect if a or b is zero, denormal, infinity, or NaN.
+    if (aExponent-1U >= maxExponent-1U || bExponent-1U >= maxExponent-1U) {
+        
+        const rep_t aAbs = toRep(a) & absMask;
+        const rep_t bAbs = toRep(b) & absMask;
+        
+        // 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 * non-zero = +/- infinity
+            if (bAbs) return fromRep(aAbs | productSign);
+            // infinity * zero = NaN
+            else return fromRep(qnanRep);
+        }
+        
+        if (bAbs == infRep) {
+            // non-zero * infinity = +/- infinity
+            if (aAbs) return fromRep(bAbs | productSign);
+            // zero * infinity = NaN
+            else return fromRep(qnanRep);
+        }
+        
+        // zero * anything = +/- zero
+        if (!aAbs) return fromRep(productSign);
+        // anything * zero = +/- zero
+        if (!bAbs) return fromRep(productSign);
+        
+        // one or both of a or b is denormal, the other (if applicable) is a
+        // normal number.  Renormalize one or both of a and b, and set scale to
+        // include the necessary exponent adjustment.
+        if (aAbs < implicitBit) scale += normalize(&aSignificand);
+        if (bAbs < implicitBit) scale += normalize(&bSignificand);
+    }
+    
+    // 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 |= implicitBit;
+    bSignificand |= implicitBit;
+    
+    // Get the significand of a*b.  Before multiplying the significands, shift
+    // one of them left to left-align it in the field.  Thus, the product will
+    // have (exponentBits + 2) integral digits, all but two of which must be
+    // zero.  Normalizing this result is just a conditional left-shift by one
+    // and bumping the exponent accordingly.
+    rep_t productHi, productLo;
+    wideMultiply(aSignificand, bSignificand << exponentBits,
+                 &productHi, &productLo);
+    
+    int productExponent = aExponent + bExponent - exponentBias + scale;
+    
+    // Normalize the significand, adjust exponent if needed.
+    if (productHi & implicitBit) productExponent++;
+    else wideLeftShift(&productHi, &productLo, 1);
+    
+    // If we have overflowed the type, return +/- infinity.
+    if (productExponent >= maxExponent) return fromRep(infRep | productSign);
+    
+    if (productExponent <= 0) {
+        // Result is denormal before rounding
+        //
+        // If the result is so small that it just underflows to zero, return
+        // a zero of the appropriate sign.  Mathematically there is no need to
+        // handle this case separately, but we make it a special case to
+        // simplify the shift logic.
+        const int shift = 1 - productExponent;
+        if (shift >= typeWidth) return fromRep(productSign);
+        
+        // Otherwise, shift the significand of the result so that the round
+        // bit is the high bit of productLo.
+        wideRightShiftWithSticky(&productHi, &productLo, shift);
+    }
+    
+    else {
+        // Result is normal before rounding; insert the exponent.
+        productHi &= significandMask;
+        productHi |= (rep_t)productExponent << significandBits;
+    }
+    
+    // Insert the sign of the result:
+    productHi |= productSign;
+    
+    // Final rounding.  The final result may overflow to infinity, or underflow
+    // to zero, but those are the correct results in those cases.  We use the
+    // default IEEE-754 round-to-nearest, ties-to-even rounding mode.
+    if (productLo > signBit) productHi++;
+    if (productLo == signBit) productHi += productHi & 1;
+    return fromRep(productHi);
+}