ea1a60faa3
git-svn-id: svn://kolibrios.org@9837 a494cfbc-eb01-0410-851d-a64ba20cac60
204 lines
6.5 KiB
C
204 lines
6.5 KiB
C
/**
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* Decode a Game Genie code into an M68000 address/data pair.
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* The Game Genie code is made of the characters
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* ABCDEFGHJKLMNPRSTVWXYZ0123456789 (notice the missing I, O, Q and U).
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* Where A = 00000, B = 00001, C = 00010, ... , on to 9 = 11111.
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*
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* These come out to a very scrambled bit pattern like this:
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* (SCRA-MBLE is just an example)
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*
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* S C R A - M B L E
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* 01111 00010 01110 00000 01011 00001 01010 00100
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* ijklm nopIJ KLMNO PABCD EFGHd efgha bcQRS TUVWX
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*
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* Our goal is to rearrange that to this:
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*
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* 0000 0101 1001 1100 0100 0100 : 1011 0000 0111 1000
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* ABCD EFGH IJKL MNOP QRST UVWX : abcd efgh ijkl mnop
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*
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* which in Hexadecimal is 059C44:B078. Simple, huh? ;)
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*
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* So, then, we dutifully change memory location 059C44 to B078!
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* (of course, that's handled by a different source file :)
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*/
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#include <stdio.h>
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#include <string.h>
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#include "decode.h"
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static char genie_chars[] = "AaBbCcDdEeFfGgHhJjKkLlMmNnPpRrSsTtVvWwXxYyZz0O1I2233445566778899";
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/**
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* Decode a Game Genie Code.
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* This function converts a Game Genie code to an address:data pair.
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* The code is given as an 8-character string, like "BJX0SA1C". It need not
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* be null terminated, since only the first 8 characters are taken. It is
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* assumed that the code is already made of valid characters, i.e. there are no
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* Q's, U's, or symbols. If such a character is
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* encountered, the function will return with a warning on stderr.
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*
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* The resulting address:data pair is returned in the struct patch pointed to
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* by result. If an error results, both the address and data will be set to -1.
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*
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* @param[in] code 8 character Game Genie code.
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* @param[out] result The resulting address:data pair is returned in the struct
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* patch pointed to by result. If an error results, both the address and data
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* will be set to -1.
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*/
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void genie_decode(const char *code, struct patch *result)
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{
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int i = 0, n;
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char* x;
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for(; i < 8; ++i)
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{
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/* If strchr returns NULL, we were given a bad character */
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if(!(x = strchr(genie_chars, code[i])))
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{
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result->addr = -1; result->data = -1;
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return;
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}
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n = (x - genie_chars) >> 1;
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/* Now, based on which character this is, fit it into the result */
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switch(i)
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{
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case 0:
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/* ____ ____ ____ ____ ____ ____ : ____ ____ ABCD E___ */
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result->data |= n << 3;
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break;
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case 1:
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/* ____ ____ DE__ ____ ____ ____ : ____ ____ ____ _ABC */
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result->data |= n >> 2;
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result->addr |= (n & 3) << 14;
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break;
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case 2:
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/* ____ ____ __AB CDE_ ____ ____ : ____ ____ ____ ____ */
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result->addr |= n << 9;
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break;
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case 3:
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/* BCDE ____ ____ ___A ____ ____ : ____ ____ ____ ____ */
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result->addr |= (n & 0xF) << 20 | (n >> 4) << 8;
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break;
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case 4:
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/* ____ ABCD ____ ____ ____ ____ : ___E ____ ____ ____ */
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result->data |= (n & 1) << 12;
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result->addr |= (n >> 1) << 16;
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break;
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case 5:
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/* ____ ____ ____ ____ ____ ____ : E___ ABCD ____ ____ */
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result->data |= (n & 1) << 15 | (n >> 1) << 8;
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break;
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case 6:
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/* ____ ____ ____ ____ CDE_ ____ : _AB_ ____ ____ ____ */
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result->data |= (n >> 3) << 13;
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result->addr |= (n & 7) << 5;
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break;
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case 7:
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/* ____ ____ ____ ____ ___A BCDE : ____ ____ ____ ____ */
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result->addr |= n;
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break;
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}
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/* Go around again */
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}
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return;
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}
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/**
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* "Decode" an address/data pair into a structure. This is for "012345:ABCD"
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* type codes. You're more likely to find Genie codes circulating around, but
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* there's a chance you could come on to one of these. Which is nice, since
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* they're MUCH easier to implement ;) Once again, the input should be
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* depunctuated already.
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*
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* @param[in] code 8 character Game Genie code.
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* @param[out] result The resulting address:data pair is returned in the struct
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* patch pointed to by result. If an error results, both the address and data
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* will be set to -1.
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*/
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void hex_decode(const char *code, struct patch *result)
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{
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static char hex_chars[] = "00112233445566778899AaBbCcDdEeFf";
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char *x;
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int i;
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/* 6 digits for address */
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for(i = 0; i < 6; ++i)
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{
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if(!(x = strchr(hex_chars, code[i])))
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{
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result->addr = result->data = -1;
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return;
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}
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result->addr = (result->addr << 4) | ((x - hex_chars) >> 1);
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}
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/* 4 digits for data */
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for(i = 6; i < 10; ++i)
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{
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if(!(x = strchr(hex_chars, code[i])))
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{
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result->addr = result->data = -1;
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return;
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}
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result->data = (result->data << 4) | ((x - hex_chars) >> 1);
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}
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}
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/**
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* THIS is the function you call from the MegaDrive or whatever. This figures
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* out whether it's a genie or hex code, depunctuates it, and calls the proper
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* decoder.
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*
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* @param[in] code Game Genie or hex code.
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* @param[out] result The resulting address:data pair is returned in the struct
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* patch pointed to by result. If an error results, both the address and data
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* will be set to -1.
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*/
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void decode(const char *code, struct patch *result)
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{
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int len = strlen(code), i, j;
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char code_to_pass[16], *x;
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const char *ad, *da;
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int adl, dal;
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/* Initialize the result */
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result->addr = result->data = 0;
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/* If it's 9 chars long and the 5th is a hyphen, we have a Game Genie
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* code. */
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if(len == 9 && code[4] == '-')
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{
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/* Remove the hyphen and pass to genie_decode */
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code_to_pass[0] = code[0];
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code_to_pass[1] = code[1];
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code_to_pass[2] = code[2];
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code_to_pass[3] = code[3];
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code_to_pass[4] = code[5];
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code_to_pass[5] = code[6];
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code_to_pass[6] = code[7];
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code_to_pass[7] = code[8];
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code_to_pass[8] = '\0';
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genie_decode(code_to_pass, result);
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return;
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}
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/* Otherwise, we assume it's a hex code.
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* Find the colon so we know where address ends and data starts. If there's
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* no colon, then we haven't a code at all! */
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if(!(x = strchr(code, ':'))) goto bad_code;
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ad = code; da = x + 1; adl = x - code; dal = len - adl - 1;
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/* If a section is empty or too long, toss it */
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if(adl == 0 || adl > 6 || dal == 0 || dal > 4) goto bad_code;
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/* Pad the address with zeros, then fill it with the value */
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for(i = 0; i < (6 - adl); ++i) code_to_pass[i] = '0';
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for(j = 0; i < 6; ++i, ++j) code_to_pass[i] = ad[j];
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/* Do the same for data */
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for(i = 6; i < (10 - dal); ++i) code_to_pass[i] = '0';
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for(j = 0; i < 10; ++i, ++j) code_to_pass[i] = da[j];
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code_to_pass[10] = '\0';
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/* Decode and goodbye */
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hex_decode(code_to_pass, result);
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return;
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bad_code:
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/* AGH! Invalid code! */
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result->data = result->addr = -1;
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return;
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}
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