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-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This file implements a fairly generic conversion from a narrower to a wider 10// IEEE-754 floating-point type. The constants and types defined following the 11// includes below parameterize the conversion. 12// 13// It does not support types that don't use the usual IEEE-754 interchange 14// formats; specifically, some work would be needed to adapt it to 15// (for example) the Intel 80-bit format or PowerPC double-double format. 16// 17// Note please, however, that this implementation is only intended to support 18// *widening* operations; if you need to convert to a *narrower* floating-point 19// type (e.g. double -> float), then this routine will not do what you want it 20// to. 21// 22// It also requires that integer types at least as large as both formats 23// are available on the target platform; this may pose a problem when trying 24// to add support for quad on some 32-bit systems, for example. You also may 25// 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 the 31// target platform. 32// 33// 2. Quiet NaNs, if supported, are indicated by the leading bit of the 34// 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-bit 41// format. In particular, for the source type srcSigFracBits may be not equal to 42// srcSigBits. The destination type is assumed to be one of IEEE-754 standard 43// 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 all 79 // the non-significand bits are zero. In particular, this branch is always 80 // 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_clz 85 // If src_rep_t_clz is not defined this branch must be unreachable. 86 __builtin_unreachable(); 87#else 88 // 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)srcSigFrac 93 << (dstSigFracBits - srcSigFracBits + scale); 94 const dst_rep_t dstMinNormal = DST_REP_C(1) << (dstBits - 1 - dstExpBits); 95 dstSigFrac ^= dstMinNormal; 96#endif 97 } 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