div.c

linux0.02源代码用于研究linux操作系统

/*
 * linux/kernel/math/div.c
 *
 * (C) 1991 Linus Torvalds
 */

/*
 * temporary real division routine.
 */

#include <linux/math_emu.h>

static void shift_left(int * c)
{
	__asm__ __volatile__("movl (%0),%%eax ; addl %%eax,(%0)\n\t"
		"movl 4(%0),%%eax ; adcl %%eax,4(%0)\n\t"
		"movl 8(%0),%%eax ; adcl %%eax,8(%0)\n\t"
		"movl 12(%0),%%eax ; adcl %%eax,12(%0)"
		::"r" ((long) c):"ax");
}

static void shift_right(int * c)
{
	__asm__("shrl $1,12(%0) ; rcrl $1,8(%0) ; rcrl $1,4(%0) ; rcrl $1,(%0)"
		::"r" ((long) c));
}

static int try_sub(int * a, int * b)
{
	char ok;

	__asm__ __volatile__("movl (%1),%%eax ; subl %%eax,(%2)\n\t"
		"movl 4(%1),%%eax ; sbbl %%eax,4(%2)\n\t"
		"movl 8(%1),%%eax ; sbbl %%eax,8(%2)\n\t"
		"movl 12(%1),%%eax ; sbbl %%eax,12(%2)\n\t"
		"setae %%al":"=a" (ok):"c" ((long) a),"d" ((long) b));
	return ok;
}

static void div64(int * a, int * b, int * c)
{
	int tmp[4];
	int i;
	unsigned int mask = 0;

	c += 4;
	for (i = 0 ; i<64 ; i++) {
		if (!(mask >>= 1)) {
			c--;
			mask = 0x80000000;
		}
		tmp[0] = a[0]; tmp[1] = a[1];
		tmp[2] = a[2]; tmp[3] = a[3];
		if (try_sub(b,tmp)) {
			*c |= mask;
			a[0] = tmp[0]; a[1] = tmp[1];
			a[2] = tmp[2]; a[3] = tmp[3];
		}
		shift_right(b);
	}
}

void fdiv(const temp_real * src1, const temp_real * src2, temp_real * result)
{
	int i,sign;
	int a[4],b[4],tmp[4] = {0,0,0,0};

	sign = (src1->exponent ^ src2->exponent) & 0x8000;
	if (!(src2->a || src2->b)) {
		set_ZE();
		return;
	}
	i = (src1->exponent & 0x7fff) - (src2->exponent & 0x7fff) + 16383;
	if (i<0) {
		set_UE();
		result->exponent = sign;
		result->a = result->b = 0;
		return;
	}
	a[0] = a[1] = 0;
	a[2] = src1->a;
	a[3] = src1->b;
	b[0] = b[1] = 0;
	b[2] = src2->a;
	b[3] = src2->b;
	while (b[3] >= 0) {
		i++;
		shift_left(b);
	}
	div64(a,b,tmp);
	if (tmp[0] || tmp[1] || tmp[2] || tmp[3]) {
		while (i && tmp[3] >= 0) {
			i--;
			shift_left(tmp);
		}
		if (tmp[3] >= 0)
			set_DE();
	} else
		i = 0;
	if (i>0x7fff) {
		set_OE();
		return;
	}
	if (tmp[0] || tmp[1])
		set_PE();
	result->exponent = i | sign;
	result->a = tmp[2];
	result->b = tmp[3];
}