Vendor import of llvm-project main 8e464dd76bef, the last commit beforevendor/llvm-project/llvmorg-12-init-17869-g8e464dd76bef

the upstream release/12.x branch was created.

1 files changed, 5 insertions, 169 deletions

diff --git a/compiler-rt/lib/builtins/divsf3.c b/compiler-rt/lib/builtins/divsf3.c
index 593f93b45ac2..5744c015240b 100644
--- a/compiler-rt/lib/builtins/divsf3.c
+++ b/compiler-rt/lib/builtins/divsf3.c
@@ -9,181 +9,17 @@
 // This file implements single-precision soft-float division
 // with the IEEE-754 default rounding (to nearest, ties to even).
 //
-// For simplicity, this implementation currently flushes denormals to zero.
-// It should be a fairly straightforward exercise to implement gradual
-// underflow with correct rounding.
-//
 //===----------------------------------------------------------------------===//
 
 #define SINGLE_PRECISION
-#include "fp_lib.h"
-
-COMPILER_RT_ABI fp_t __divsf3(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 quotientSign = (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 / infinity = NaN
-      if (bAbs == infRep)
-        return fromRep(qnanRep);
-      // infinity / anything else = +/- infinity
-      else
-        return fromRep(aAbs | quotientSign);
-    }
-
-    // anything else / infinity = +/- 0
-    if (bAbs == infRep)
-      return fromRep(quotientSign);
-
-    if (!aAbs) {
-      // zero / zero = NaN
-      if (!bAbs)
-        return fromRep(qnanRep);
-      // zero / anything else = +/- zero
-      else
-        return fromRep(quotientSign);
-    }
-    // anything else / zero = +/- infinity
-    if (!bAbs)
-      return fromRep(infRep | quotientSign);
-
-    // 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);
-  }
-
-  // Set 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;
-  int quotientExponent = aExponent - bExponent + scale;
-  // 0x7504F333 / 2^32 + 1 = 3/4 + 1/sqrt(2)
-
-  // Align the significand of b as a Q31 fixed-point number in the range
-  // [1, 2.0) and get a Q32 approximate reciprocal using a small minimax
-  // polynomial approximation: reciprocal = 3/4 + 1/sqrt(2) - b/2.  This
-  // is accurate to about 3.5 binary digits.
-  uint32_t q31b = bSignificand << 8;
-  uint32_t reciprocal = UINT32_C(0x7504f333) - q31b;
-
-  // Now refine the reciprocal estimate using a Newton-Raphson iteration:
-  //
-  //     x1 = x0 * (2 - x0 * b)
-  //
-  // This doubles the number of correct binary digits in the approximation
-  // with each iteration.
-  uint32_t correction;
-  correction = -((uint64_t)reciprocal * q31b >> 32);
-  reciprocal = (uint64_t)reciprocal * correction >> 31;
-  correction = -((uint64_t)reciprocal * q31b >> 32);
-  reciprocal = (uint64_t)reciprocal * correction >> 31;
-  correction = -((uint64_t)reciprocal * q31b >> 32);
-  reciprocal = (uint64_t)reciprocal * correction >> 31;
-
-  // Adust the final 32-bit reciprocal estimate downward to ensure that it is
-  // strictly smaller than the infinitely precise exact reciprocal.  Because
-  // the computation of the Newton-Raphson step is truncating at every step,
-  // this adjustment is small; most of the work is already done.
-  reciprocal -= 2;
-
-  // The numerical reciprocal is accurate to within 2^-28, lies in the
-  // interval [0x1.000000eep-1, 0x1.fffffffcp-1], and is strictly smaller
-  // than the true reciprocal of b.  Multiplying a by this reciprocal thus
-  // gives a numerical q = a/b in Q24 with the following properties:
-  //
-  //    1. q < a/b
-  //    2. q is in the interval [0x1.000000eep-1, 0x1.fffffffcp0)
-  //    3. The error in q is at most 2^-24 + 2^-27 -- the 2^24 term comes
-  //       from the fact that we truncate the product, and the 2^27 term
-  //       is the error in the reciprocal of b scaled by the maximum
-  //       possible value of a.  As a consequence of this error bound,
-  //       either q or nextafter(q) is the correctly rounded.
-  rep_t quotient = (uint64_t)reciprocal * (aSignificand << 1) >> 32;
-
-  // Two cases: quotient is in [0.5, 1.0) or quotient is in [1.0, 2.0).
-  // In either case, we are going to compute a residual of the form
-  //
-  //     r = a - q*b
-  //
-  // We know from the construction of q that r satisfies:
-  //
-  //     0 <= r < ulp(q)*b
-  //
-  // If r is greater than 1/2 ulp(q)*b, then q rounds up.  Otherwise, we
-  // already have the correct result.  The exact halfway case cannot occur.
-  // We also take this time to right shift quotient if it falls in the [1,2)
-  // range and adjust the exponent accordingly.
-  rep_t residual;
-  if (quotient < (implicitBit << 1)) {
-    residual = (aSignificand << 24) - quotient * bSignificand;
-    quotientExponent--;
-  } else {
-    quotient >>= 1;
-    residual = (aSignificand << 23) - quotient * bSignificand;
-  }
-
-  const int writtenExponent = quotientExponent + exponentBias;
 
-  if (writtenExponent >= maxExponent) {
-    // If we have overflowed the exponent, return infinity.
-    return fromRep(infRep | quotientSign);
-  }
+#define NUMBER_OF_HALF_ITERATIONS 0
+#define NUMBER_OF_FULL_ITERATIONS 3
+#define USE_NATIVE_FULL_ITERATIONS
 
-  else if (writtenExponent < 1) {
-    if (writtenExponent == 0) {
-      // Check whether the rounded result is normal.
-      const bool round = (residual << 1) > bSignificand;
-      // Clear the implicit bit.
-      rep_t absResult = quotient & significandMask;
-      // Round.
-      absResult += round;
-      if (absResult & ~significandMask) {
-        // The rounded result is normal; return it.
-        return fromRep(absResult | quotientSign);
-      }
-    }
-    // Flush denormals to zero.  In the future, it would be nice to add
-    // code to round them correctly.
-    return fromRep(quotientSign);
-  }
+#include "fp_div_impl.inc"
 
-  else {
-    const bool round = (residual << 1) > bSignificand;
-    // Clear the implicit bit.
-    rep_t absResult = quotient & significandMask;
-    // Insert the exponent.
-    absResult |= (rep_t)writtenExponent << significandBits;
-    // Round.
-    absResult += round;
-    // Insert the sign and return.
-    return fromRep(absResult | quotientSign);
-  }
-}
+COMPILER_RT_ABI fp_t __divsf3(fp_t a, fp_t b) { return __divXf3__(a, b); }
 
 #if defined(__ARM_EABI__)
 #if defined(COMPILER_RT_ARMHF_TARGET)