104 lines
1.5 KiB
C
104 lines
1.5 KiB
C
#include "os.h"
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#include <mp.h>
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#include "dat.h"
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#define LO(x) ((x) & ((1<<(Dbits/2))-1))
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#define HI(x) ((x) >> (Dbits/2))
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static void
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mpdigmul(mpdigit a, mpdigit b, mpdigit *p)
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{
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mpdigit x, ah, al, bh, bl, p1, p2, p3, p4;
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int carry;
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// half digits
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ah = HI(a);
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al = LO(a);
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bh = HI(b);
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bl = LO(b);
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// partial products
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p1 = ah*bl;
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p2 = bh*al;
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p3 = bl*al;
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p4 = ah*bh;
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// p = ((p1+p2)<<(Dbits/2)) + (p4<<Dbits) + p3
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carry = 0;
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x = p1<<(Dbits/2);
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p3 += x;
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if(p3 < x)
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carry++;
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x = p2<<(Dbits/2);
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p3 += x;
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if(p3 < x)
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carry++;
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p4 += carry + HI(p1) + HI(p2); // can't carry out of the high digit
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p[0] = p3;
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p[1] = p4;
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}
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// prereq: p must have room for n+1 digits
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void
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mpvecdigmuladd(mpdigit *b, int n, mpdigit m, mpdigit *p)
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{
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int i;
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mpdigit carry, x, y, part[2];
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carry = 0;
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part[1] = 0;
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for(i = 0; i < n; i++){
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x = part[1] + carry;
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if(x < carry)
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carry = 1;
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else
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carry = 0;
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y = *p;
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mpdigmul(*b++, m, part);
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x += part[0];
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if(x < part[0])
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carry++;
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x += y;
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if(x < y)
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carry++;
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*p++ = x;
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}
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*p = part[1] + carry;
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}
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// prereq: p must have room for n+1 digits
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int
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mpvecdigmulsub(mpdigit *b, int n, mpdigit m, mpdigit *p)
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{
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int i;
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mpdigit x, y, part[2], borrow;
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borrow = 0;
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part[1] = 0;
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for(i = 0; i < n; i++){
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x = *p;
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y = x - borrow;
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if(y > x)
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borrow = 1;
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else
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borrow = 0;
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x = part[1];
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mpdigmul(*b++, m, part);
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x += part[0];
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if(x < part[0])
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borrow++;
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x = y - x;
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if(x > y)
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borrow++;
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*p++ = x;
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}
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x = *p;
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y = x - borrow - part[1];
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*p = y;
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if(y > x)
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return -1;
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else
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return 1;
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}
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