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658716d19f
The current implementation of div64_u64 for 32bit systems returns an approximately correct result when the divisor exceeds 32bits. Since doing 64bit division using 32bit hardware is a long since solved problem we just use one of the existing proven methods. Additionally, add a div64_s64 function to correctly handle doing signed 64bit division. Addresses https://bugzilla.redhat.com/show_bug.cgi?id=616105 Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Ben Woodard <bwoodard@llnl.gov> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Mark Grondona <mgrondona@llnl.gov> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
143 lines
3.1 KiB
C
143 lines
3.1 KiB
C
/*
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* Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
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*
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* Based on former do_div() implementation from asm-parisc/div64.h:
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* Copyright (C) 1999 Hewlett-Packard Co
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* Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
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*
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*
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* Generic C version of 64bit/32bit division and modulo, with
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* 64bit result and 32bit remainder.
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*
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* The fast case for (n>>32 == 0) is handled inline by do_div().
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*
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* Code generated for this function might be very inefficient
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* for some CPUs. __div64_32() can be overridden by linking arch-specific
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* assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
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*/
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#include <linux/module.h>
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#include <linux/math64.h>
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/* Not needed on 64bit architectures */
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#if BITS_PER_LONG == 32
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uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
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{
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uint64_t rem = *n;
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uint64_t b = base;
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uint64_t res, d = 1;
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uint32_t high = rem >> 32;
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/* Reduce the thing a bit first */
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res = 0;
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if (high >= base) {
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high /= base;
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res = (uint64_t) high << 32;
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rem -= (uint64_t) (high*base) << 32;
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}
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while ((int64_t)b > 0 && b < rem) {
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b = b+b;
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d = d+d;
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}
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do {
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if (rem >= b) {
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rem -= b;
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res += d;
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}
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b >>= 1;
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d >>= 1;
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} while (d);
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*n = res;
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return rem;
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}
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EXPORT_SYMBOL(__div64_32);
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#ifndef div_s64_rem
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s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
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{
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u64 quotient;
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if (dividend < 0) {
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quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
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*remainder = -*remainder;
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if (divisor > 0)
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quotient = -quotient;
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} else {
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quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
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if (divisor < 0)
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quotient = -quotient;
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}
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return quotient;
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}
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EXPORT_SYMBOL(div_s64_rem);
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#endif
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/**
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* div64_u64 - unsigned 64bit divide with 64bit divisor
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* @dividend: 64bit dividend
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* @divisor: 64bit divisor
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*
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* This implementation is a modified version of the algorithm proposed
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* by the book 'Hacker's Delight'. The original source and full proof
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* can be found here and is available for use without restriction.
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*
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* 'http://www.hackersdelight.org/HDcode/newCode/divDouble.c'
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*/
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#ifndef div64_u64
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u64 div64_u64(u64 dividend, u64 divisor)
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{
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u32 high = divisor >> 32;
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u64 quot;
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if (high == 0) {
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quot = div_u64(dividend, divisor);
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} else {
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int n = 1 + fls(high);
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quot = div_u64(dividend >> n, divisor >> n);
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if (quot != 0)
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quot--;
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if ((dividend - quot * divisor) >= divisor)
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quot++;
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}
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return quot;
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}
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EXPORT_SYMBOL(div64_u64);
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#endif
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/**
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* div64_s64 - signed 64bit divide with 64bit divisor
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* @dividend: 64bit dividend
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* @divisor: 64bit divisor
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*/
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#ifndef div64_s64
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s64 div64_s64(s64 dividend, s64 divisor)
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{
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s64 quot, t;
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quot = div64_u64(abs64(dividend), abs64(divisor));
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t = (dividend ^ divisor) >> 63;
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return (quot ^ t) - t;
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}
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EXPORT_SYMBOL(div64_s64);
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#endif
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#endif /* BITS_PER_LONG == 32 */
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/*
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* Iterative div/mod for use when dividend is not expected to be much
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* bigger than divisor.
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*/
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u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
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{
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return __iter_div_u64_rem(dividend, divisor, remainder);
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}
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EXPORT_SYMBOL(iter_div_u64_rem);
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