forked from OSchip/llvm-project
96 lines
3.3 KiB
C++
96 lines
3.3 KiB
C++
//===-- int_div_impl.inc - Integer division ---------------------*- C++ -*-===//
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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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// Helpers used by __udivsi3, __umodsi3, __udivdi3, and __umodsi3.
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//
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//===----------------------------------------------------------------------===//
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#define clz(a) (sizeof(a) == sizeof(unsigned long long) ? __builtin_clzll(a) : clzsi(a))
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// Adapted from Figure 3-40 of The PowerPC Compiler Writer's Guide
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static __inline fixuint_t __udivXi3(fixuint_t n, fixuint_t d) {
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const unsigned N = sizeof(fixuint_t) * CHAR_BIT;
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// d == 0 cases are unspecified.
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unsigned sr = (d ? clz(d) : N) - (n ? clz(n) : N);
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// 0 <= sr <= N - 1 or sr is very large.
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if (sr > N - 1) // n < d
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return 0;
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if (sr == N - 1) // d == 1
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return n;
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++sr;
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// 1 <= sr <= N - 1. Shifts do not trigger UB.
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fixuint_t r = n >> sr;
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n <<= N - sr;
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fixuint_t carry = 0;
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for (; sr > 0; --sr) {
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r = (r << 1) | (n >> (N - 1));
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n = (n << 1) | carry;
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// Branch-less version of:
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// carry = 0;
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// if (r >= d) r -= d, carry = 1;
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const fixint_t s = (fixint_t)(d - r - 1) >> (N - 1);
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carry = s & 1;
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r -= d & s;
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}
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n = (n << 1) | carry;
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return n;
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}
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// Mostly identical to __udivXi3 but the return values are different.
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static __inline fixuint_t __umodXi3(fixuint_t n, fixuint_t d) {
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const unsigned N = sizeof(fixuint_t) * CHAR_BIT;
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// d == 0 cases are unspecified.
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unsigned sr = (d ? clz(d) : N) - (n ? clz(n) : N);
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// 0 <= sr <= N - 1 or sr is very large.
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if (sr > N - 1) // n < d
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return n;
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if (sr == N - 1) // d == 1
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return 0;
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++sr;
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// 1 <= sr <= N - 1. Shifts do not trigger UB.
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fixuint_t r = n >> sr;
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n <<= N - sr;
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fixuint_t carry = 0;
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for (; sr > 0; --sr) {
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r = (r << 1) | (n >> (N - 1));
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n = (n << 1) | carry;
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// Branch-less version of:
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// carry = 0;
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// if (r >= d) r -= d, carry = 1;
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const fixint_t s = (fixint_t)(d - r - 1) >> (N - 1);
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carry = s & 1;
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r -= d & s;
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}
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return r;
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}
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#ifdef COMPUTE_UDIV
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static __inline fixint_t __divXi3(fixint_t a, fixint_t b) {
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const int N = (int)(sizeof(fixint_t) * CHAR_BIT) - 1;
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fixint_t s_a = a >> N; // s_a = a < 0 ? -1 : 0
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fixint_t s_b = b >> N; // s_b = b < 0 ? -1 : 0
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fixuint_t a_u = (fixuint_t)(a ^ s_a) + (-s_a); // negate if s_a == -1
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fixuint_t b_u = (fixuint_t)(b ^ s_b) + (-s_b); // negate if s_b == -1
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s_a ^= s_b; // sign of quotient
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return (COMPUTE_UDIV(a_u, b_u) ^ s_a) + (-s_a); // negate if s_a == -1
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}
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#endif // COMPUTE_UDIV
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#ifdef ASSIGN_UMOD
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static __inline fixint_t __modXi3(fixint_t a, fixint_t b) {
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const int N = (int)(sizeof(fixint_t) * CHAR_BIT) - 1;
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fixint_t s = b >> N; // s = b < 0 ? -1 : 0
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fixuint_t b_u = (fixuint_t)(b ^ s) + (-s); // negate if s == -1
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s = a >> N; // s = a < 0 ? -1 : 0
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fixuint_t a_u = (fixuint_t)(a ^ s) + (-s); // negate if s == -1
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fixuint_t res;
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ASSIGN_UMOD(res, a_u, b_u);
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return (res ^ s) + (-s); // negate if s == -1
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}
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#endif // ASSIGN_UMOD
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