Fix compiler runtime for _Float16 type

third_party/compiler_rt/fp16_trunc_impl.inc

@@ -0,0 +1,155 @@
+//= lib/fp_trunc_impl.inc - high precision -> low precision conversion *-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a fairly generic conversion from a wider to a narrower
+// IEEE-754 floating-point type in the default (round to nearest, ties to even)
+// rounding mode.  The constants and types defined following the includes below
+// parameterize the conversion.
+//
+// This routine can be trivially adapted to support conversions to
+// half-precision or from quad-precision. It does not support types that don't
+// use the usual IEEE-754 interchange formats; specifically, some work would be
+// needed to adapt it to (for example) the Intel 80-bit format or PowerPC
+// double-double format.
+//
+// Note please, however, that this implementation is only intended to support
+// *narrowing* operations; if you need to convert to a *wider* floating-point
+// type (e.g. float -> double), then this routine will not do what you want it
+// to.
+//
+// It also requires that integer types at least as large as both formats
+// are available on the target platform; this may pose a problem when trying
+// to add support for quad on some 32-bit systems, for example.
+//
+// Finally, the following assumptions are made:
+//
+// 1. Floating-point types and integer types have the same endianness on the
+//    target platform.
+//
+// 2. Quiet NaNs, if supported, are indicated by the leading bit of the
+//    significand field being set.
+//
+//===----------------------------------------------------------------------===//
+
+#include "fp16_trunc.inc"
+
+// The destination type may use a usual IEEE-754 interchange format or Intel
+// 80-bit format. In particular, for the destination type dstSigFracBits may be
+// not equal to dstSigBits. The source type is assumed to be one of IEEE-754
+// standard types.
+static __inline dst_t __truncXfYf2__(src_t a) {
+  // Various constants whose values follow from the type parameters.
+  // Any reasonable optimizer will fold and propagate all of these.
+  const int srcInfExp = (1 << srcExpBits) - 1;
+  const int srcExpBias = srcInfExp >> 1;
+
+  const src_rep_t srcMinNormal = SRC_REP_C(1) << srcSigFracBits;
+  const src_rep_t roundMask =
+      (SRC_REP_C(1) << (srcSigFracBits - dstSigFracBits)) - 1;
+  const src_rep_t halfway = SRC_REP_C(1)
+                            << (srcSigFracBits - dstSigFracBits - 1);
+  const src_rep_t srcQNaN = SRC_REP_C(1) << (srcSigFracBits - 1);
+  const src_rep_t srcNaNCode = srcQNaN - 1;
+
+  const int dstInfExp = (1 << dstExpBits) - 1;
+  const int dstExpBias = dstInfExp >> 1;
+  const int overflowExponent = srcExpBias + dstInfExp - dstExpBias;
+
+  const dst_rep_t dstQNaN = DST_REP_C(1) << (dstSigFracBits - 1);
+  const dst_rep_t dstNaNCode = dstQNaN - 1;
+
+  const src_rep_t aRep = srcToRep(a);
+  const src_rep_t srcSign = extract_sign_from_src(aRep);
+  const src_rep_t srcExp = extract_exp_from_src(aRep);
+  const src_rep_t srcSigFrac = extract_sig_frac_from_src(aRep);
+
+  dst_rep_t dstSign = srcSign;
+  dst_rep_t dstExp;
+  dst_rep_t dstSigFrac;
+
+  // Same size exponents and a's significand tail is 0.
+  // The significand can be truncated and the exponent can be copied over.
+  const int sigFracTailBits = srcSigFracBits - dstSigFracBits;
+  if (srcExpBits == dstExpBits &&
+      ((aRep >> sigFracTailBits) << sigFracTailBits) == aRep) {
+    dstExp = srcExp;
+    dstSigFrac = (dst_rep_t)(srcSigFrac >> sigFracTailBits);
+    return dstFromRep(construct_dst_rep(dstSign, dstExp, dstSigFrac));
+  }
+
+  const int dstExpCandidate = ((int)srcExp - srcExpBias) + dstExpBias;
+  if (dstExpCandidate >= 1 && dstExpCandidate < dstInfExp) {
+    // The exponent of a is within the range of normal numbers in the
+    // destination format. We can convert by simply right-shifting with
+    // rounding and adjusting the exponent.
+    dstExp = dstExpCandidate;
+    dstSigFrac = (dst_rep_t)(srcSigFrac >> sigFracTailBits);
+
+    const src_rep_t roundBits = srcSigFrac & roundMask;
+    // Round to nearest.
+    if (roundBits > halfway)
+      dstSigFrac++;
+    // Tie to even.
+    else if (roundBits == halfway)
+      dstSigFrac += dstSigFrac & 1;
+
+    // Rounding has changed the exponent.
+    if (dstSigFrac >= (DST_REP_C(1) << dstSigFracBits)) {
+      dstExp += 1;
+      dstSigFrac ^= (DST_REP_C(1) << dstSigFracBits);
+    }
+  } else if (srcExp == srcInfExp && srcSigFrac) {
+    // a is NaN.
+    // Conjure the result by beginning with infinity, setting the qNaN
+    // bit and inserting the (truncated) trailing NaN field.
+    dstExp = dstInfExp;
+    dstSigFrac = dstQNaN;
+    dstSigFrac |= ((srcSigFrac & srcNaNCode) >> sigFracTailBits) & dstNaNCode;
+  } else if ((int)srcExp >= overflowExponent) {
+    dstExp = dstInfExp;
+    dstSigFrac = 0;
+  } else {
+    // a underflows on conversion to the destination type or is an exact
+    // zero.  The result may be a denormal or zero.  Extract the exponent
+    // to get the shift amount for the denormalization.
+    src_rep_t significand = srcSigFrac;
+    int shift = srcExpBias - dstExpBias - srcExp;
+
+    if (srcExp) {
+      // Set the implicit integer bit if the source is a normal number.
+      significand |= srcMinNormal;
+      shift += 1;
+    }
+
+    // Right shift by the denormalization amount with sticky.
+    if (shift > srcSigFracBits) {
+      dstExp = 0;
+      dstSigFrac = 0;
+    } else {
+      dstExp = 0;
+      const bool sticky = shift && ((significand << (srcBits - shift)) != 0);
+      src_rep_t denormalizedSignificand = significand >> shift | sticky;
+      dstSigFrac = denormalizedSignificand >> sigFracTailBits;
+      const src_rep_t roundBits = denormalizedSignificand & roundMask;
+      // Round to nearest
+      if (roundBits > halfway)
+        dstSigFrac++;
+      // Ties to even
+      else if (roundBits == halfway)
+        dstSigFrac += dstSigFrac & 1;
+
+      // Rounding has changed the exponent.
+      if (dstSigFrac >= (DST_REP_C(1) << dstSigFracBits)) {
+        dstExp += 1;
+        dstSigFrac ^= (DST_REP_C(1) << dstSigFracBits);
+      }
+    }
+  }
+
+  return dstFromRep(construct_dst_rep(dstSign, dstExp, dstSigFrac));
+}