initial version

Book-Lite/linux-0.12/kernel/math/div.c

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+/*
+ * 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];
+}