88 lines
2 KiB
C
88 lines
2 KiB
C
/* div64() - full 64-bit division */
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/* rem64() - full 64-bit modulo */
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/* Author: Erik van der Kouwe */
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/* 14 May 2010 */
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#include <assert.h>
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#include <minix/u64.h>
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static u32_t shl64hi(u64_t i, unsigned shift)
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{
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/* compute the high-order 32-bit value in (i << shift) */
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if (shift == 0)
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return i.hi;
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else if (shift < 32)
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return (i.hi << shift) | (i.lo >> (32 - shift));
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else if (shift == 32)
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return i.lo;
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else if (shift < 64)
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return i.lo << (shift - 32);
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else
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return 0;
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}
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static u64_t divrem64(u64_t *i, u64_t j)
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{
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u32_t i32, j32, q;
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u64_t result = { 0, 0 };
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unsigned shift;
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assert(i);
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/* this function is not suitable for small divisors */
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assert(ex64hi(j) != 0);
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/* as long as i >= j we work on reducing i */
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while (cmp64(*i, j) >= 0) {
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/* shift to obtain the 32 most significant bits */
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shift = 63 - bsr64(*i);
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i32 = shl64hi(*i, shift);
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j32 = shl64hi(j, shift);
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/* find a lower bound for *i/j */
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if (j32 + 1 < j32) {
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/* avoid overflow, since *i >= j we know q >= 1 */
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q = 1;
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} else {
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/* use 32-bit division, round j32 up to ensure that
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* we obtain a lower bound
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*/
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q = i32 / (j32 + 1);
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/* since *i >= j we know q >= 1 */
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if (q < 1) q = 1;
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}
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/* perform the division using the lower bound we found */
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*i = sub64(*i, mul64(j, cvu64(q)));
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result = add64u(result, q);
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}
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/* if we get here then *i < j; because we round down we are finished */
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return result;
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}
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u64_t div64(u64_t i, u64_t j)
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{
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/* divrem64 is unsuitable for small divisors, especially zero which would
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* trigger a infinite loop; use assembly function in this case
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*/
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if (!ex64hi(j)) {
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return div64u64(i, ex64lo(j));
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}
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return divrem64(&i, j);
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}
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u64_t rem64(u64_t i, u64_t j)
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{
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/* divrem64 is unsuitable for small divisors, especially zero which would
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* trigger a infinite loop; use assembly function in this case
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*/
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if (!ex64hi(j)) {
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return cvu64(rem64u(i, ex64lo(j)));
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}
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divrem64(&i, j);
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return i;
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}
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