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51835dfadb
MSVC in C mode apparently doesn't consider `const int` to be sufficiently constant expression This was broken in #66903.
73 lines
2.7 KiB
C++
73 lines
2.7 KiB
C++
//===-- int_to_fp_impl.inc - integer to floating point conversion ---------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Thsi file implements a generic conversion from an integer type to an
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// IEEE-754 floating point type, allowing a common implementation to be hsared
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// without copy and paste.
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//
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//===----------------------------------------------------------------------===//
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#include "int_to_fp.h"
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static __inline dst_t __floatXiYf__(src_t a) {
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if (a == 0)
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return 0.0;
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enum {
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dstMantDig = dstSigBits + 1,
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srcBits = sizeof(src_t) * CHAR_BIT,
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srcIsSigned = ((src_t)-1) < 0,
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};
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const src_t s = srcIsSigned ? a >> (srcBits - 1) : 0;
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a = (usrc_t)(a ^ s) - s;
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int sd = srcBits - clzSrcT(a); // number of significant digits
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int e = sd - 1; // exponent
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if (sd > dstMantDig) {
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// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
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// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
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// 12345678901234567890123456
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// 1 = msb 1 bit
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// P = bit dstMantDig-1 bits to the right of 1
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// Q = bit dstMantDig bits to the right of 1
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// R = "or" of all bits to the right of Q
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if (sd == dstMantDig + 1) {
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a <<= 1;
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} else if (sd == dstMantDig + 2) {
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// Do nothing.
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} else {
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a = ((usrc_t)a >> (sd - (dstMantDig + 2))) |
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((a & ((usrc_t)(-1) >> ((srcBits + dstMantDig + 2) - sd))) != 0);
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}
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// finish:
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a |= (a & 4) != 0; // Or P into R
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++a; // round - this step may add a significant bit
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a >>= 2; // dump Q and R
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// a is now rounded to dstMantDig or dstMantDig+1 bits
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if (a & ((usrc_t)1 << dstMantDig)) {
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a >>= 1;
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++e;
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}
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// a is now rounded to dstMantDig bits
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} else {
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a <<= (dstMantDig - sd);
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// a is now rounded to dstMantDig bits
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}
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const int dstBits = sizeof(dst_t) * CHAR_BIT;
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const dst_rep_t dstSignMask = DST_REP_C(1) << (dstBits - 1);
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const int dstExpBits = dstBits - dstSigBits - 1;
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const int dstExpBias = (1 << (dstExpBits - 1)) - 1;
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const dst_rep_t dstSignificandMask = (DST_REP_C(1) << dstSigBits) - 1;
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// Combine sign, exponent, and mantissa.
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const dst_rep_t result = ((dst_rep_t)s & dstSignMask) |
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((dst_rep_t)(e + dstExpBias) << dstSigBits) |
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((dst_rep_t)(a) & dstSignificandMask);
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return dstFromRep(result);
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}
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