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udivmodti4.c
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udivmodti4.c
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//===-- udivmodti4.c - Implement __udivmodti4 -----------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements __udivmodti4 for the compiler_rt library.
//
//===----------------------------------------------------------------------===//
#include "int_lib.h"
#ifdef CRT_HAS_128BIT
// Effects: if rem != 0, *rem = a % b
// Returns: a / b
// Translated from Figure 3-40 of The PowerPC Compiler Writer's Guide
COMPILER_RT_ABI tu_int __udivmodti4(tu_int a, tu_int b, tu_int *rem) {
const unsigned n_udword_bits = sizeof(du_int) * CHAR_BIT;
const unsigned n_utword_bits = sizeof(tu_int) * CHAR_BIT;
utwords n;
n.all = a;
utwords d;
d.all = b;
utwords q;
utwords r;
unsigned sr;
// special cases, X is unknown, K != 0
if (n.s.high == 0) {
if (d.s.high == 0) {
// 0 X
// ---
// 0 X
if (rem)
*rem = n.s.low % d.s.low;
return n.s.low / d.s.low;
}
// 0 X
// ---
// K X
if (rem)
*rem = n.s.low;
return 0;
}
// n.s.high != 0
if (d.s.low == 0) {
if (d.s.high == 0) {
// K X
// ---
// 0 0
if (rem)
*rem = n.s.high % d.s.low;
return n.s.high / d.s.low;
}
// d.s.high != 0
if (n.s.low == 0) {
// K 0
// ---
// K 0
if (rem) {
r.s.high = n.s.high % d.s.high;
r.s.low = 0;
*rem = r.all;
}
return n.s.high / d.s.high;
}
// K K
// ---
// K 0
if ((d.s.high & (d.s.high - 1)) == 0) /* if d is a power of 2 */ {
if (rem) {
r.s.low = n.s.low;
r.s.high = n.s.high & (d.s.high - 1);
*rem = r.all;
}
return n.s.high >> __builtin_ctzll(d.s.high);
}
// K K
// ---
// K 0
sr = __builtin_clzll(d.s.high) - __builtin_clzll(n.s.high);
// 0 <= sr <= n_udword_bits - 2 or sr large
if (sr > n_udword_bits - 2) {
if (rem)
*rem = n.all;
return 0;
}
++sr;
// 1 <= sr <= n_udword_bits - 1
// q.all = n.all << (n_utword_bits - sr);
q.s.low = 0;
q.s.high = n.s.low << (n_udword_bits - sr);
// r.all = n.all >> sr;
r.s.high = n.s.high >> sr;
r.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
} else /* d.s.low != 0 */ {
if (d.s.high == 0) {
// K X
// ---
// 0 K
if ((d.s.low & (d.s.low - 1)) == 0) /* if d is a power of 2 */ {
if (rem)
*rem = n.s.low & (d.s.low - 1);
if (d.s.low == 1)
return n.all;
sr = __builtin_ctzll(d.s.low);
q.s.high = n.s.high >> sr;
q.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
return q.all;
}
// K X
// ---
// 0 K
sr = 1 + n_udword_bits + __builtin_clzll(d.s.low) -
__builtin_clzll(n.s.high);
// 2 <= sr <= n_utword_bits - 1
// q.all = n.all << (n_utword_bits - sr);
// r.all = n.all >> sr;
if (sr == n_udword_bits) {
q.s.low = 0;
q.s.high = n.s.low;
r.s.high = 0;
r.s.low = n.s.high;
} else if (sr < n_udword_bits) /* 2 <= sr <= n_udword_bits - 1 */ {
q.s.low = 0;
q.s.high = n.s.low << (n_udword_bits - sr);
r.s.high = n.s.high >> sr;
r.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
} else /* n_udword_bits + 1 <= sr <= n_utword_bits - 1 */ {
q.s.low = n.s.low << (n_utword_bits - sr);
q.s.high = (n.s.high << (n_utword_bits - sr)) |
(n.s.low >> (sr - n_udword_bits));
r.s.high = 0;
r.s.low = n.s.high >> (sr - n_udword_bits);
}
} else {
// K X
// ---
// K K
sr = __builtin_clzll(d.s.high) - __builtin_clzll(n.s.high);
// 0 <= sr <= n_udword_bits - 1 or sr large
if (sr > n_udword_bits - 1) {
if (rem)
*rem = n.all;
return 0;
}
++sr;
// 1 <= sr <= n_udword_bits
// q.all = n.all << (n_utword_bits - sr);
// r.all = n.all >> sr;
q.s.low = 0;
if (sr == n_udword_bits) {
q.s.high = n.s.low;
r.s.high = 0;
r.s.low = n.s.high;
} else {
r.s.high = n.s.high >> sr;
r.s.low = (n.s.high << (n_udword_bits - sr)) | (n.s.low >> sr);
q.s.high = n.s.low << (n_udword_bits - sr);
}
}
}
// Not a special case
// q and r are initialized with:
// q.all = n.all << (n_utword_bits - sr);
// r.all = n.all >> sr;
// 1 <= sr <= n_utword_bits - 1
su_int carry = 0;
for (; sr > 0; --sr) {
// r:q = ((r:q) << 1) | carry
r.s.high = (r.s.high << 1) | (r.s.low >> (n_udword_bits - 1));
r.s.low = (r.s.low << 1) | (q.s.high >> (n_udword_bits - 1));
q.s.high = (q.s.high << 1) | (q.s.low >> (n_udword_bits - 1));
q.s.low = (q.s.low << 1) | carry;
// carry = 0;
// if (r.all >= d.all)
// {
// r.all -= d.all;
// carry = 1;
// }
const ti_int s = (ti_int)(d.all - r.all - 1) >> (n_utword_bits - 1);
carry = s & 1;
r.all -= d.all & s;
}
q.all = (q.all << 1) | carry;
if (rem)
*rem = r.all;
return q.all;
}
#endif // CRT_HAS_128BIT