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1//=-lib/fp_extend_impl.inc - low precision -> high precision conversion -*-- -//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This file implements a fairly generic conversion from a narrower to a wider10// IEEE-754 floating-point type. The constants and types defined following the11// includes below parameterize the conversion.12//13// It does not support types that don't use the usual IEEE-754 interchange14// formats; specifically, some work would be needed to adapt it to15// (for example) the Intel 80-bit format or PowerPC double-double format.16//17// Note please, however, that this implementation is only intended to support18// *widening* operations; if you need to convert to a *narrower* floating-point19// type (e.g. double -> float), then this routine will not do what you want it20// to.21//22// It also requires that integer types at least as large as both formats23// are available on the target platform; this may pose a problem when trying24// to add support for quad on some 32-bit systems, for example. You also may25// run into trouble finding an appropriate CLZ function for wide source types;26// you will likely need to roll your own on some platforms.27//28// Finally, the following assumptions are made:29//30// 1. Floating-point types and integer types have the same endianness on the31// target platform.32//33// 2. Quiet NaNs, if supported, are indicated by the leading bit of the34// significand field being set.35//36//===----------------------------------------------------------------------===//37 38#include "fp_extend.h"39 40// The source type may use a usual IEEE-754 interchange format or Intel 80-bit41// format. In particular, for the source type srcSigFracBits may be not equal to42// srcSigBits. The destination type is assumed to be one of IEEE-754 standard43// types.44static __inline dst_t __extendXfYf2__(src_t a) {45 // Various constants whose values follow from the type parameters.46 // Any reasonable optimizer will fold and propagate all of these.47 const int srcInfExp = (1 << srcExpBits) - 1;48 const int srcExpBias = srcInfExp >> 1;49 50 const int dstInfExp = (1 << dstExpBits) - 1;51 const int dstExpBias = dstInfExp >> 1;52 53 // Break a into a sign and representation of the absolute value.54 const src_rep_t aRep = srcToRep(a);55 const src_rep_t srcSign = extract_sign_from_src(aRep);56 const src_rep_t srcExp = extract_exp_from_src(aRep);57 const src_rep_t srcSigFrac = extract_sig_frac_from_src(aRep);58 59 dst_rep_t dstSign = srcSign;60 dst_rep_t dstExp;61 dst_rep_t dstSigFrac;62 63 if (srcExp >= 1 && srcExp < (src_rep_t)srcInfExp) {64 // a is a normal number.65 dstExp = (dst_rep_t)srcExp + (dst_rep_t)(dstExpBias - srcExpBias);66 dstSigFrac = (dst_rep_t)srcSigFrac << (dstSigFracBits - srcSigFracBits);67 }68 69 else if (srcExp == srcInfExp) {70 // a is NaN or infinity.71 dstExp = dstInfExp;72 dstSigFrac = (dst_rep_t)srcSigFrac << (dstSigFracBits - srcSigFracBits);73 }74 75 else if (srcSigFrac) {76 // a is denormal.77 if (srcExpBits == dstExpBits) {78 // The exponent fields are identical and this is a denormal number, so all79 // the non-significand bits are zero. In particular, this branch is always80 // taken when we extend a denormal F80 to F128.81 dstExp = 0;82 dstSigFrac = ((dst_rep_t)srcSigFrac) << (dstSigFracBits - srcSigFracBits);83 } else {84#ifndef src_rep_t_clz85 // If src_rep_t_clz is not defined this branch must be unreachable.86 __builtin_unreachable();87#else88 // Renormalize the significand and clear the leading bit.89 // For F80 -> F128 this codepath is unused.90 const int scale = clz_in_sig_frac(srcSigFrac) + 1;91 dstExp = dstExpBias - srcExpBias - scale + 1;92 dstSigFrac = (dst_rep_t)srcSigFrac93 << (dstSigFracBits - srcSigFracBits + scale);94 const dst_rep_t dstMinNormal = DST_REP_C(1) << (dstBits - 1 - dstExpBits);95 dstSigFrac ^= dstMinNormal;96#endif97 }98 }99 100 else {101 // a is zero.102 dstExp = 0;103 dstSigFrac = 0;104 }105 106 const dst_rep_t result = construct_dst_rep(dstSign, dstExp, dstSigFrac);107 return dstFromRep(result);108}109