diff options
Diffstat (limited to 'cpukit/compiler-rt/lib/builtins/int_div_impl.inc')
| -rw-r--r-- | cpukit/compiler-rt/lib/builtins/int_div_impl.inc | 95 |
1 files changed, 95 insertions, 0 deletions
diff --git a/cpukit/compiler-rt/lib/builtins/int_div_impl.inc b/cpukit/compiler-rt/lib/builtins/int_div_impl.inc new file mode 100644 index 0000000000..dc1f97cbea --- /dev/null +++ b/cpukit/compiler-rt/lib/builtins/int_div_impl.inc @@ -0,0 +1,95 @@ +//===-- int_div_impl.inc - Integer division ---------------------*- C++ -*-===// +// +// 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 +// +//===----------------------------------------------------------------------===// +// +// Helpers used by __udivsi3, __umodsi3, __udivdi3, and __umodsi3. +// +//===----------------------------------------------------------------------===// + +#define clz(a) (sizeof(a) == sizeof(unsigned long long) ? __builtin_clzll(a) : clzsi(a)) + +// Adapted from Figure 3-40 of The PowerPC Compiler Writer's Guide +static __inline fixuint_t __udivXi3(fixuint_t n, fixuint_t d) { + const unsigned N = sizeof(fixuint_t) * CHAR_BIT; + // d == 0 cases are unspecified. + unsigned sr = (d ? clz(d) : N) - (n ? clz(n) : N); + // 0 <= sr <= N - 1 or sr is very large. + if (sr > N - 1) // n < d + return 0; + if (sr == N - 1) // d == 1 + return n; + ++sr; + // 1 <= sr <= N - 1. Shifts do not trigger UB. + fixuint_t r = n >> sr; + n <<= N - sr; + fixuint_t carry = 0; + for (; sr > 0; --sr) { + r = (r << 1) | (n >> (N - 1)); + n = (n << 1) | carry; + // Branch-less version of: + // carry = 0; + // if (r >= d) r -= d, carry = 1; + const fixint_t s = (fixint_t)(d - r - 1) >> (N - 1); + carry = s & 1; + r -= d & s; + } + n = (n << 1) | carry; + return n; +} + +// Mostly identical to __udivXi3 but the return values are different. +static __inline fixuint_t __umodXi3(fixuint_t n, fixuint_t d) { + const unsigned N = sizeof(fixuint_t) * CHAR_BIT; + // d == 0 cases are unspecified. + unsigned sr = (d ? clz(d) : N) - (n ? clz(n) : N); + // 0 <= sr <= N - 1 or sr is very large. + if (sr > N - 1) // n < d + return n; + if (sr == N - 1) // d == 1 + return 0; + ++sr; + // 1 <= sr <= N - 1. Shifts do not trigger UB. + fixuint_t r = n >> sr; + n <<= N - sr; + fixuint_t carry = 0; + for (; sr > 0; --sr) { + r = (r << 1) | (n >> (N - 1)); + n = (n << 1) | carry; + // Branch-less version of: + // carry = 0; + // if (r >= d) r -= d, carry = 1; + const fixint_t s = (fixint_t)(d - r - 1) >> (N - 1); + carry = s & 1; + r -= d & s; + } + return r; +} + +#ifdef COMPUTE_UDIV +static __inline fixint_t __divXi3(fixint_t a, fixint_t b) { + const int N = (int)(sizeof(fixint_t) * CHAR_BIT) - 1; + fixint_t s_a = a >> N; // s_a = a < 0 ? -1 : 0 + fixint_t s_b = b >> N; // s_b = b < 0 ? -1 : 0 + fixuint_t a_u = (fixuint_t)(a ^ s_a) + (-s_a); // negate if s_a == -1 + fixuint_t b_u = (fixuint_t)(b ^ s_b) + (-s_b); // negate if s_b == -1 + s_a ^= s_b; // sign of quotient + return (COMPUTE_UDIV(a_u, b_u) ^ s_a) + (-s_a); // negate if s_a == -1 +} +#endif // COMPUTE_UDIV + +#ifdef ASSIGN_UMOD +static __inline fixint_t __modXi3(fixint_t a, fixint_t b) { + const int N = (int)(sizeof(fixint_t) * CHAR_BIT) - 1; + fixint_t s = b >> N; // s = b < 0 ? -1 : 0 + fixuint_t b_u = (fixuint_t)(b ^ s) + (-s); // negate if s == -1 + s = a >> N; // s = a < 0 ? -1 : 0 + fixuint_t a_u = (fixuint_t)(a ^ s) + (-s); // negate if s == -1 + fixuint_t res; + ASSIGN_UMOD(res, a_u, b_u); + return (res ^ s) + (-s); // negate if s == -1 +} +#endif // ASSIGN_UMOD |