2.1.7. Macro Expansion¶

Within the code of Zlib, infback9.c has few macros. Let’s see an example of NEEDBITS.

#define NEEDBITS(n)                         \
    do {                                    \
        while (bits < (unsigned)(n))        \
            PULLBYTE();                     \
    } while (0)

But. the macro NEEDBITS depends on PULLBYTE

#define PULLBYTE()                                \
    do {                                          \
        PULL();                                   \
        have--;                                   \
        hold += (unsigned long)(*next++) << bits; \
        bits += 8;                                \
    } while (0)

The dependencies continue.

#define PULL()                              \
    do {                                    \
        if (have == 0) {                    \
            have = in(in_desc, &next);      \
            if (have == 0) {                \
                next = Z_NULL;              \
                ret = Z_BUF_ERROR;          \
                goto inf_leave;             \
            }                               \
        }                                   \
    } while (0)

#define Z_NULL  0

#define Z_BUF_ERROR    (-5)