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lib/div64.c 1.28 KB
1da177e4c   Linus Torvalds   Linux-2.6.12-rc2
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  /*
   * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
   *
   * Based on former do_div() implementation from asm-parisc/div64.h:
   *	Copyright (C) 1999 Hewlett-Packard Co
   *	Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
   *
   *
   * Generic C version of 64bit/32bit division and modulo, with
   * 64bit result and 32bit remainder.
   *
   * The fast case for (n>>32 == 0) is handled inline by do_div(). 
   *
   * Code generated for this function might be very inefficient
   * for some CPUs. __div64_32() can be overridden by linking arch-specific
   * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
   */
  
  #include <linux/types.h>
  #include <linux/module.h>
  #include <asm/div64.h>
  
  /* Not needed on 64bit architectures */
  #if BITS_PER_LONG == 32
  
  uint32_t __div64_32(uint64_t *n, uint32_t base)
  {
  	uint64_t rem = *n;
  	uint64_t b = base;
  	uint64_t res, d = 1;
  	uint32_t high = rem >> 32;
  
  	/* Reduce the thing a bit first */
  	res = 0;
  	if (high >= base) {
  		high /= base;
  		res = (uint64_t) high << 32;
  		rem -= (uint64_t) (high*base) << 32;
  	}
  
  	while ((int64_t)b > 0 && b < rem) {
  		b = b+b;
  		d = d+d;
  	}
  
  	do {
  		if (rem >= b) {
  			rem -= b;
  			res += d;
  		}
  		b >>= 1;
  		d >>= 1;
  	} while (d);
  
  	*n = res;
  	return rem;
  }
  
  EXPORT_SYMBOL(__div64_32);
  
  #endif /* BITS_PER_LONG == 32 */