multiply.c

来自「skyeye的开源代码」· C语言 代码 · 共 85 行

#include "emul.h"
// Perform long multiplication of x by y.

extern MIPS_State * mstate;

void 
multiply_UInt64(UInt64 u, UInt64 v)
{
    	UInt64 u0 = bits(u, 31,  0);
    	UInt64 u1 = bits(u, 63, 32);

    	UInt64 v0 = bits(v, 31,  0);
    	UInt64 v1 = bits(v, 63, 32);

    	UInt64 w0 = 0;
    	UInt64 w1 = 0;
    	UInt64 w2;
    	UInt64 w3;

    	UInt64 t, k;

    	k = 0;

    	// i == 0, j == 0
    	t  = u0 * v0 + w0 + k;
    	w0 = bits(t, 31,  0);
    	k  = bits(t, 63, 32);

    	// i == 1, j == 0
    	t  = u1 * v0 + w1 + k;
    	w1 = bits(t, 31,  0);
    	k  = bits(t, 63, 32);

    	w2 = k;
    	k  = 0;

    	// i == 0, j == 1
    	t  = u0 * v1 + w1 + k;
    	w1 = bits(t, 31,  0);
    	k  = bits(t, 63, 32);

    	// j == 1, i == 1
    	t  = u1 * v1 + w2 + k;
    	w2 = bits(t, 31,  0);
    	k  = bits(t, 63, 32);

    	w3 = k;

    	// Glue the bits back into full words.
    	mstate->lo = w0 | (w1 << 32);
    	mstate->hi = w2 | (w3 << 32);
}

void 
multiply_Int64(Int64 u, Int64 v)
{
    	// Compute the sign of the result;
    	int neg;
    	if (u < 0) {
		if (v < 0) {
	    		neg =0;
	    		v = -v;
		} else {
	    		neg = 1;
		}
		u = -u;
    	} else {
		if (v < 0) {
	    	neg = 1;
	    	v = -v;
		} else {
	   		 neg =0;
		}
    	}
    	multiply_UInt64((UInt64)u, (UInt64)v);
    	if (neg) {
		mstate->lo = ~mstate->lo;
		mstate->hi = ~mstate->hi;
		if (++mstate->lo == 0) {
	    		++mstate->hi;
		}
    	}
}