Fix signedness mistakes in secp256k1_num_set_hex #56

1. 
   sipa commented at 1:43 pm on August 26, 2014: contributor

   Closes #51 as well.
2. sipa renamed this:
   Fix some signedness mistakes in secp256k1_num_set_hex
   Fix signedness mistakes in secp256k1_num_set_hex
   on Aug 26, 2014
3. sipa cross-referenced this on Aug 26, 2014 from issue fix unsigned warning in num_gmp_impl.h by caktux
4. 
   caktux commented at 5:09 pm on August 26, 2014: contributor

   This does not fix the warning, casting to unsigned later or declaring as unsigned while assigning to signed is the same mistake. Here the type passed to mpn_set_str is unsigned char*.

   0.../secp256k1/impl/num_gmp.h:286:37: warning: passing 'char [257]' to parameter of type 'const unsigned char *' converts between pointers to integer types with different sign [-Wpointer-sign]
   1    r->limbs = mpn_set_str(r->data, num, alen, 16);
   2                                    ^~~
   3/usr/local/include/gmp.h:1585:68: note: passing argument to parameter here
   4__GMP_DECLSPEC mp_size_t mpn_set_str (mp_ptr, const unsigned char *, size_t, int);
   5                                                                   ^
   

5. 
   sipa commented at 11:16 pm on August 26, 2014: contributor

   You’re right. I found some online documentation that declared it as const char_, but it seems my version here also uses const unsigned char_.
6. Fix a signedness mistake in secp256k1_num_set_hex

   We were using a potentially signed char as index in an array.

   fa492f059d
7. sipa force-pushed on Aug 26, 2014
8. 
   sipa commented at 11:54 pm on August 26, 2014: contributor

   Merged #51, and rebased this to only fix the array indexing.
9. sipa merged this on Aug 28, 2014
10. sipa closed this on Aug 28, 2014

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11. sipa referenced this in commit d531b04ea9 on Aug 28, 2014
12. real-or-random referenced this in commit acc62885b5 on May 31, 2019

Contributors
sipa caktux