bb0548a6ed
When compiling compiler-rt with -fsanitize=undefined and running testcases you end up with the following warning: UBSan: floatdisf.c:27:15: signed integer overflow: 9223372036854775807 - -1 cannot be represented in type 'di_int' (aka 'long long') This can be avoided by doing the subtraction in a matching unsigned variant of the type, given that the overflow is the expected result of the subtraction. The same kind of pattern exists in floatdidf.c This was found in an out of tree target. Reviewed By: phosek Differential Revision: https://reviews.llvm.org/D146135
108 lines
3.5 KiB
C
108 lines
3.5 KiB
C
//===-- floatdidf.c - Implement __floatdidf -------------------------------===//
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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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// This file implements __floatdidf for the compiler_rt library.
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//
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//===----------------------------------------------------------------------===//
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#include "int_lib.h"
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// Returns: convert a to a double, rounding toward even.
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// Assumption: double is a IEEE 64 bit floating point type
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// di_int is a 64 bit integral type
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// seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
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// mmmm
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#ifndef __SOFTFP__
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// Support for systems that have hardware floating-point; we'll set the inexact
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// flag as a side-effect of this computation.
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COMPILER_RT_ABI double __floatdidf(di_int a) {
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static const double twop52 = 4503599627370496.0; // 0x1.0p52
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static const double twop32 = 4294967296.0; // 0x1.0p32
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union {
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int64_t x;
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double d;
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} low = {.d = twop52};
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const double high = (int32_t)(a >> 32) * twop32;
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low.x |= a & INT64_C(0x00000000ffffffff);
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const double result = (high - twop52) + low.d;
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return result;
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}
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#else
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// Support for systems that don't have hardware floating-point; there are no
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// flags to set, and we don't want to code-gen to an unknown soft-float
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// implementation.
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COMPILER_RT_ABI double __floatdidf(di_int a) {
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if (a == 0)
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return 0.0;
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const unsigned N = sizeof(di_int) * CHAR_BIT;
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const di_int s = a >> (N - 1);
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a = (du_int)(a ^ s) - s;
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int sd = N - __builtin_clzll(a); // number of significant digits
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int e = sd - 1; // exponent
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if (sd > DBL_MANT_DIG) {
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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 DBL_MANT_DIG-1 bits to the right of 1
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// Q = bit DBL_MANT_DIG bits to the right of 1
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// R = "or" of all bits to the right of Q
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switch (sd) {
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case DBL_MANT_DIG + 1:
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a <<= 1;
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break;
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case DBL_MANT_DIG + 2:
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break;
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default:
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a = ((du_int)a >> (sd - (DBL_MANT_DIG + 2))) |
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((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG + 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 DBL_MANT_DIG or DBL_MANT_DIG+1 bits
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if (a & ((du_int)1 << DBL_MANT_DIG)) {
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a >>= 1;
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++e;
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}
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// a is now rounded to DBL_MANT_DIG bits
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} else {
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a <<= (DBL_MANT_DIG - sd);
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// a is now rounded to DBL_MANT_DIG bits
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}
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double_bits fb;
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fb.u.s.high = ((su_int)s & 0x80000000) | // sign
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((su_int)(e + 1023) << 20) | // exponent
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((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high
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fb.u.s.low = (su_int)a; // mantissa-low
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return fb.f;
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}
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#endif
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#if defined(__ARM_EABI__)
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#if defined(COMPILER_RT_ARMHF_TARGET)
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AEABI_RTABI double __aeabi_l2d(di_int a) { return __floatdidf(a); }
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#else
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COMPILER_RT_ALIAS(__floatdidf, __aeabi_l2d)
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#endif
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#endif
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#if defined(__MINGW32__) && defined(__arm__)
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COMPILER_RT_ALIAS(__floatdidf, __i64tod)
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#endif
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