hex_code.c

[詳解]

/*++
/* NAME
/*  hex_code 3
/* SUMMARY
/*  encode/decode data, hexadecimal style
/* SYNOPSIS
/*  #include <hex_code.h>
/*
/*  VSTRING *hex_encode(result, in, len)
/*  VSTRING *result;
/*  const char *in;
/*  ssize_t len;
/*
/*  VSTRING *hex_decode(result, in, len)
/*  VSTRING *result;
/*  const char *in;
/*  ssize_t len;
/* DESCRIPTION
/*  hex_encode() takes a block of len bytes and encodes it as one
/*  upper-case null-terminated string.  The result value is
/*  the result argument.
/*
/*  hex_decode() performs the opposite transformation on
/*  lower-case, upper-case or mixed-case input. The result
/*  value is the result argument. The result is null terminated,
/*  whether or not that makes sense.
/* DIAGNOSTICS
/*  hex_decode() returns a null pointer when the input contains
/*  characters not in the hexadecimal alphabet.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <ctype.h>
#include <string.h>

/* Utility library. */

#include <msg.h>
#include <mymalloc.h>
#include <vstring.h>
#include <hex_code.h>

/* Application-specific. */

static const unsigned char hex_chars[] = "0123456789ABCDEF";

#define UCHAR_PTR(x) ((const unsigned char *)(x))

/* hex_encode - raw data to encoded */

VSTRING *hex_encode(VSTRING *result, const char *in, ssize_t len)
{
    const unsigned char *cp;
    int     ch;
    ssize_t count;

    VSTRING_RESET(result);
    for (cp = UCHAR_PTR(in), count = len; count > 0; count--, cp++) {
    ch = *cp;
    VSTRING_ADDCH(result, hex_chars[(ch >> 4) & 0xf]);
    VSTRING_ADDCH(result, hex_chars[ch & 0xf]);
    }
    VSTRING_TERMINATE(result);
    return (result);
}

/* hex_decode - encoded data to raw */

VSTRING *hex_decode(VSTRING *result, const char *in, ssize_t len)
{
    const unsigned char *cp;
    ssize_t count;
    unsigned int hex;
    unsigned int bin;

    VSTRING_RESET(result);
    for (cp = UCHAR_PTR(in), count = len; count > 0; cp += 2, count -= 2) {
    if (count < 2)
        return (0);
    hex = cp[0];
    if (hex >= '0' && hex <= '9')
        bin = (hex - '0') << 4;
    else if (hex >= 'A' && hex <= 'F')
        bin = (hex - 'A' + 10) << 4;
    else if (hex >= 'a' && hex <= 'f')
        bin = (hex - 'a' + 10) << 4;
    else
        return (0);
    hex = cp[1];
    if (hex >= '0' && hex <= '9')
        bin |= (hex - '0');
    else if (hex >= 'A' && hex <= 'F')
        bin |= (hex - 'A' + 10);
    else if (hex >= 'a' && hex <= 'f')
        bin |= (hex - 'a' + 10);
    else
        return (0);
    VSTRING_ADDCH(result, bin);
    }
    VSTRING_TERMINATE(result);
    return (result);
}

#ifdef TEST

 /*
  * Proof-of-concept test program: convert to hexadecimal and back.
  */

#define STR(x)  vstring_str(x)
#define LEN(x)  VSTRING_LEN(x)

int     main(int unused_argc, char **unused_argv)
{
    VSTRING *b1 = vstring_alloc(1);
    VSTRING *b2 = vstring_alloc(1);
    char   *test = "this is a test";

#define DECODE(b,x,l) { \
    if (hex_decode((b),(x),(l)) == 0) \
        msg_panic("bad hex: %s", (x)); \
    }
#define VERIFY(b,t) { \
    if (strcmp((b), (t)) != 0) \
        msg_panic("bad test: %s", (b)); \
    }

    hex_encode(b1, test, strlen(test));
    DECODE(b2, STR(b1), LEN(b1));
    VERIFY(STR(b2), test);

    hex_encode(b1, test, strlen(test));
    hex_encode(b2, STR(b1), LEN(b1));
    hex_encode(b1, STR(b2), LEN(b2));
    DECODE(b2, STR(b1), LEN(b1));
    DECODE(b1, STR(b2), LEN(b2));
    DECODE(b2, STR(b1), LEN(b1));
    VERIFY(STR(b2), test);

    hex_encode(b1, test, strlen(test));
    hex_encode(b2, STR(b1), LEN(b1));
    hex_encode(b1, STR(b2), LEN(b2));
    hex_encode(b2, STR(b1), LEN(b1));
    hex_encode(b1, STR(b2), LEN(b2));
    DECODE(b2, STR(b1), LEN(b1));
    DECODE(b1, STR(b2), LEN(b2));
    DECODE(b2, STR(b1), LEN(b1));
    DECODE(b1, STR(b2), LEN(b2));
    DECODE(b2, STR(b1), LEN(b1));
    VERIFY(STR(b2), test);

    vstring_free(b1);
    vstring_free(b2);
    return (0);
}

#endif