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//===-- int_to_fp_impl.inc - integer to floating point 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
//
//===----------------------------------------------------------------------===//
//
// Thsi file implements a generic conversion from an integer type to an
// IEEE-754 floating point type, allowing a common implementation to be hsared
// without copy and paste.
//
//===----------------------------------------------------------------------===//
#include "int_to_fp.h"
static __inline dst_t __floatXiYf__(src_t a) {
if (a == 0)
return 0.0;
enum {
dstMantDig = dstSigBits + 1,
srcBits = sizeof(src_t) * CHAR_BIT,
srcIsSigned = ((src_t)-1) < 0,
};
const src_t s = srcIsSigned ? a >> (srcBits - 1) : 0;
a = (usrc_t)(a ^ s) - s;
int sd = srcBits - clzSrcT(a); // number of significant digits
int e = sd - 1; // exponent
if (sd > dstMantDig) {
// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
// 12345678901234567890123456
// 1 = msb 1 bit
// P = bit dstMantDig-1 bits to the right of 1
// Q = bit dstMantDig bits to the right of 1
// R = "or" of all bits to the right of Q
if (sd == dstMantDig + 1) {
a <<= 1;
} else if (sd == dstMantDig + 2) {
// Do nothing.
} else {
a = ((usrc_t)a >> (sd - (dstMantDig + 2))) |
((a & ((usrc_t)(-1) >> ((srcBits + dstMantDig + 2) - sd))) != 0);
}
// finish:
a |= (a & 4) != 0; // Or P into R
++a; // round - this step may add a significant bit
a >>= 2; // dump Q and R
// a is now rounded to dstMantDig or dstMantDig+1 bits
if (a & ((usrc_t)1 << dstMantDig)) {
a >>= 1;
++e;
}
// a is now rounded to dstMantDig bits
} else {
a <<= (dstMantDig - sd);
// a is now rounded to dstMantDig bits
}
const int dstBits = sizeof(dst_t) * CHAR_BIT;
const dst_rep_t dstSignMask = DST_REP_C(1) << (dstBits - 1);
const int dstExpBits = dstBits - dstSigBits - 1;
const int dstExpBias = (1 << (dstExpBits - 1)) - 1;
const dst_rep_t dstSignificandMask = (DST_REP_C(1) << dstSigBits) - 1;
// Combine sign, exponent, and mantissa.
const dst_rep_t result = ((dst_rep_t)s & dstSignMask) |
((dst_rep_t)(e + dstExpBias) << dstSigBits) |
((dst_rep_t)(a) & dstSignificandMask);
return dstFromRep(result);
}
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