mptobe.c (892B)
1 #include "os.h" 2 #include <mp.h> 3 #include "dat.h" 4 5 /* convert an mpint into a big endian byte array (most significant byte first) */ 6 /* return number of bytes converted */ 7 /* if p == nil, allocate and result array */ 8 int 9 mptobe(mpint *b, uchar *p, uint n, uchar **pp) 10 { 11 int i, j, suppress; 12 mpdigit x; 13 uchar *e, *s, c; 14 15 if(p == nil){ 16 n = (b->top+1)*Dbytes; 17 p = malloc(n); 18 } 19 if(p == nil) 20 return -1; 21 if(pp != nil) 22 *pp = p; 23 memset(p, 0, n); 24 25 /* special case 0 */ 26 if(b->top == 0){ 27 if(n < 1) 28 return -1; 29 else 30 return 1; 31 } 32 33 s = p; 34 e = s+n; 35 suppress = 1; 36 for(i = b->top-1; i >= 0; i--){ 37 x = b->p[i]; 38 for(j = Dbits-8; j >= 0; j -= 8){ 39 c = x>>j; 40 if(c == 0 && suppress) 41 continue; 42 if(p >= e) 43 return -1; 44 *p++ = c; 45 suppress = 0; 46 } 47 } 48 49 /* guarantee at least one byte */ 50 if(s == p){ 51 if(p >= e) 52 return -1; 53 *p++ = 0; 54 } 55 56 return p - s; 57 }