58 lines
906 B
C
58 lines
906 B
C
#include "os.h"
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#include <mp.h>
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#include "dat.h"
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// res = b >> shift
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void
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mpright(mpint *b, int shift, mpint *res)
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{
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int d, l, r, i;
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mpdigit this, last;
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res->sign = b->sign;
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if(b->top==0){
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res->top = 0;
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return;
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}
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// a negative right shift is a left shift
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if(shift < 0){
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mpleft(b, -shift, res);
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return;
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}
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if(res != b)
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mpbits(res, b->top*Dbits - shift);
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else if(shift == 0)
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return;
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d = shift/Dbits;
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r = shift - d*Dbits;
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l = Dbits - r;
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// shift all the bits out == zero
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if(d>=b->top){
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res->sign = 1;
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res->top = 0;
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return;
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}
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// special case digit shifts
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if(r == 0){
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for(i = 0; i < b->top-d; i++)
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res->p[i] = b->p[i+d];
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} else {
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last = b->p[d];
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for(i = 0; i < b->top-d-1; i++){
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this = b->p[i+d+1];
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res->p[i] = (this<<l) | (last>>r);
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last = this;
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}
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res->p[i++] = last>>r;
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}
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res->top = i;
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res->flags |= b->flags & MPtimesafe;
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mpnorm(res);
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}
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