forked from OSchip/llvm-project
107 lines
4.5 KiB
C++
107 lines
4.5 KiB
C++
//=-lib/fp_extend_impl.inc - low precision -> high precision conversion -*-- -//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is dual licensed under the MIT and the University of Illinois Open
|
|
// Source Licenses. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements a fairly generic conversion from a narrower to a wider
|
|
// IEEE-754 floating-point type. The constants and types defined following the
|
|
// includes below parameterize the conversion.
|
|
//
|
|
// 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
|
|
// *widening* operations; if you need to convert to a *narrower* floating-point
|
|
// type (e.g. double -> float), 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. You also may
|
|
// run into trouble finding an appropriate CLZ function for wide source types;
|
|
// you will likely need to roll your own on some platforms.
|
|
//
|
|
// 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 "fp_extend.h"
|
|
|
|
static inline dst_t __extendXfYf2__(src_t a) {
|
|
// Various constants whose values follow from the type parameters.
|
|
// Any reasonable optimizer will fold and propagate all of these.
|
|
const int srcBits = sizeof(src_t)*CHAR_BIT;
|
|
const int srcExpBits = srcBits - srcSigBits - 1;
|
|
const int srcInfExp = (1 << srcExpBits) - 1;
|
|
const int srcExpBias = srcInfExp >> 1;
|
|
|
|
const src_rep_t srcMinNormal = SRC_REP_C(1) << srcSigBits;
|
|
const src_rep_t srcInfinity = (src_rep_t)srcInfExp << srcSigBits;
|
|
const src_rep_t srcSignMask = SRC_REP_C(1) << (srcSigBits + srcExpBits);
|
|
const src_rep_t srcAbsMask = srcSignMask - 1;
|
|
const src_rep_t srcQNaN = SRC_REP_C(1) << (srcSigBits - 1);
|
|
const src_rep_t srcNaNCode = srcQNaN - 1;
|
|
|
|
const int dstBits = sizeof(dst_t)*CHAR_BIT;
|
|
const int dstExpBits = dstBits - dstSigBits - 1;
|
|
const int dstInfExp = (1 << dstExpBits) - 1;
|
|
const int dstExpBias = dstInfExp >> 1;
|
|
|
|
const dst_rep_t dstMinNormal = DST_REP_C(1) << dstSigBits;
|
|
|
|
// Break a into a sign and representation of the absolute value
|
|
const src_rep_t aRep = srcToRep(a);
|
|
const src_rep_t aAbs = aRep & srcAbsMask;
|
|
const src_rep_t sign = aRep & srcSignMask;
|
|
dst_rep_t absResult;
|
|
|
|
if (aAbs - srcMinNormal < srcInfinity - srcMinNormal) {
|
|
// a is a normal number.
|
|
// Extend to the destination type by shifting the significand and
|
|
// exponent into the proper position and rebiasing the exponent.
|
|
absResult = (dst_rep_t)aAbs << (dstSigBits - srcSigBits);
|
|
absResult += (dst_rep_t)(dstExpBias - srcExpBias) << dstSigBits;
|
|
}
|
|
|
|
else if (aAbs >= srcInfinity) {
|
|
// a is NaN or infinity.
|
|
// Conjure the result by beginning with infinity, then setting the qNaN
|
|
// bit (if needed) and right-aligning the rest of the trailing NaN
|
|
// payload field.
|
|
absResult = (dst_rep_t)dstInfExp << dstSigBits;
|
|
absResult |= (dst_rep_t)(aAbs & srcQNaN) << (dstSigBits - srcSigBits);
|
|
absResult |= (dst_rep_t)(aAbs & srcNaNCode) << (dstSigBits - srcSigBits);
|
|
}
|
|
|
|
else if (aAbs) {
|
|
// a is denormal.
|
|
// renormalize the significand and clear the leading bit, then insert
|
|
// the correct adjusted exponent in the destination type.
|
|
const int scale = src_rep_t_clz(aAbs) - src_rep_t_clz(srcMinNormal);
|
|
absResult = (dst_rep_t)aAbs << (dstSigBits - srcSigBits + scale);
|
|
absResult ^= dstMinNormal;
|
|
const int resultExponent = dstExpBias - srcExpBias - scale + 1;
|
|
absResult |= (dst_rep_t)resultExponent << dstSigBits;
|
|
}
|
|
|
|
else {
|
|
// a is zero.
|
|
absResult = 0;
|
|
}
|
|
|
|
// Apply the signbit to (dst_t)abs(a).
|
|
const dst_rep_t result = absResult | (dst_rep_t)sign << (dstBits - srcBits);
|
|
return dstFromRep(result);
|
|
}
|