betomp.c (589B)
1 #include "os.h" 2 #include <mp.h> 3 #include "dat.h" 4 5 /* convert a big-endian byte array (most significant byte first) to an mpint */ 6 mpint* 7 betomp(uchar *p, uint n, mpint *b) 8 { 9 int m, s; 10 mpdigit x; 11 12 if(b == nil) 13 b = mpnew(0); 14 15 /* dump leading zeros */ 16 while(*p == 0 && n > 1){ 17 p++; 18 n--; 19 } 20 21 /* get the space */ 22 mpbits(b, n*8); 23 b->top = DIGITS(n*8); 24 m = b->top-1; 25 26 /* first digit might not be Dbytes long */ 27 s = ((n-1)*8)%Dbits; 28 x = 0; 29 for(; n > 0; n--){ 30 x |= ((mpdigit)(*p++)) << s; 31 s -= 8; 32 if(s < 0){ 33 b->p[m--] = x; 34 s = Dbits-8; 35 x = 0; 36 } 37 } 38 39 return b; 40 }