pointers - wrong address value being passed to function in C -

this similar incorrect pointer value passed c function there doesn't appear answer.

i have struct, called bigint, has fields char sign, size_t len , uint32_t *val. bigints initialized bigint_init() function allocates memory uint32_t array, sets default values, etc.

i have function, void bigint_subtract(bigint a, bigint b, bigint *diff) stores a-b in diff. have tested function previously, follows:

bigint test = bigint_inithex("4567890987654345678987654adbfcaedcfaaebfc625213"); bigint test2 = bigint_inithex("acbefabedfc13271723976aebdfcabefc12837618237"); bigint diff = bigint_init(); bigint_subtract(test,test2,&diff); printf("0x%s - 0x%s == 0x%s\n\n",bigint_tohex(test), bigint_tohex(test2),bigint_tohex(diff)); 

among numerous other tests edge cases, varying lengths, etc. tests check out.

now, in function, void bigint_egcd(bigint a, bigint b, bigint c, bigint *x, bigint *y); it's extended euclidean algorithm. in main loop of extended euclidean algorithm, have following code:

bigint rold, rnew, q, r, ...; rold = bigint_init(); bigint_cpy(&rold, a); rnew = bigint_init(); bigint_cpy(&rnew, b); ...[more initializations, etc.]  while(!bigint_isval(rnew, 0)){     bigint_divide(rold,rnew,&q,&r);      bigint_cpy(&tmp1, rnew);      bigint_multiply(q,rnew,&tmp2);      bigint_subtract(rold,tmp2,&rnew);      bigint_cpy(&rold, tmp1);     .... } 

things going wrong, did debugging, couldn't figure out, started adding printfs. here's how looks now:

while(!bigint_isval(rnew, 0)){     bigint_divide(rold,rnew,&q,&r);      printf("\t%s = %s * %s + %s\n", bigint_tohex(rold), bigint_tohex(rnew), bigint_tohex(q), bigint_tohex(r));fflush(stdout);     bigint_cpy(&tmp1, rnew);      printf("\tupdated r = %s - %s * %s = ", bigint_tohex(rold), bigint_tohex(q), bigint_tohex(rnew));fflush(stdout);     bigint_multiply(q,rnew,&tmp2);      printf("%s - %s = (%p) ", bigint_tohex(rold), bigint_tohex(tmp2), &rnew);fflush(stdout);     bigint_subtract(rold,tmp2,&rnew);      printf("%s @ address %p\n", bigint_tohex(rnew),&rnew);fflush(stdout);     bigint_cpy(&rold, tmp1); 

at beginning of bigint_subtract, added following printf:

void bigint_subtract(bigint a, bigint b, bigint *diff){     printf("bigint_subtract diff address %p\n", diff);fflush(stdout);     .... 

and discovered address being received bigint_subtract not same address passing in bigint_egcd. meanwhile, subtraction correct, it's storing random address, , not updated value stored @ rnew.

meanwhile, exact same code later in loop, t , s in place of r counterparts, not exhibit behavior -- addresses passed correctly. rnew , rold initialized @ top of bigint_egcd, in same way t , s counterparts are.

in short, have variable bar1. pass &bar1 foo(type *var), somehow becomes else once inside of foo. gives? kinds of mistakes cause happen?

edit

here's bigint_tohex:

static const char *bii_hex="0123456789abcdef";  char *bigint_tohex(bigint a){     char *hex = calloc((a.len<<3) + 1,sizeof(char));     uint8_t j;     for(size_t i=0; i<a.len; i++){         for(j=0; j<8; j++){             hex[ (i<<3) + j ] = bii_hex[(a.val[i] >> ((7-j)<<2)) & 0xf];         }     }     hex[a.len<<3] = 0;      //any leading 0s should removed:     int i=0;     while(hex[i]=='0' && hex[i+1]!=0) ++i;      memmove(hex,hex+i,strlen(hex)+1-i);      if(a.sign == bii_neg){         hex = realloc(hex, (strlen(hex)+1)*sizeof(char));         memmove(hex+1,hex,strlen(hex)+1);         hex[0]='-';     }     return hex; }