47 lines
838 B
C
47 lines
838 B
C
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#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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mpleft(mpint *b, int shift, mpint *res)
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{
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int d, l, r, i, otop;
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mpdigit this, last;
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// a negative left shift is a right shift
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if(shift < 0){
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mpright(b, -shift, res);
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return;
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}
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// b and res may be the same so remember the old top
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otop = b->top;
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// shift
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mpbits(res, otop*Dbits + shift); // overkill
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res->top = DIGITS(otop*Dbits + shift);
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d = shift/Dbits;
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l = shift - d*Dbits;
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r = Dbits - l;
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if(l == 0){
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for(i = otop-1; i >= 0; i--)
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res->p[i+d] = b->p[i];
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} else {
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last = 0;
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for(i = otop-1; i >= 0; i--) {
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this = b->p[i];
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res->p[i+d+1] = (last<<l) | (this>>r);
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last = this;
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}
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res->p[d] = last<<l;
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}
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for(i = 0; i < d; i++)
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res->p[i] = 0;
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// normalize
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while(res->top > 0 && res->p[res->top-1] == 0)
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res->top--;
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}
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