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API_CHAR5.md

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mulle_char5_t

This is a encoding scheme that stashes strings that only consist of a subset of ASCII characters into integers. The actual subset is:

.ACDEINOPST_abcdefghilmnoprstuy

The values have been determined by analyzing 54674 identifiers that would not fit into 64 bit mulle_char7_t and tabulating the most popular characters.

The string "a.reason" would be transformed into a 64 bit integer like this:

   ( mulle_char5_encode_character( 'n') << (7 * 5)) |
   ( mulle_char5_encode_character( 'o') << (6 * 5)) |
   ( mulle_char5_encode_character( 's') << (5 * 5)) |
   ( mulle_char5_encode_character( 'a') << (4 * 5)) |
   ( mulle_char5_encode_character( 'e') << (3 * 5)) |
   ( mulle_char5_encode_character( 'r') << (2 * 5)) |
   ( mulle_char5_encode_character( '.') << (1 * 5)) |
   ( mulle_char5_encode_character( 'a') << (0 * 5))

On 32 bit systems the maximum string length is 6, on 64 bit systems it is 12.

Functions

mulle_char5_get

char  mulle_char5_get( mulle_char5_t value, size_t index);

Get character at index. If the index is out of range, the returned value is 0.

mulle_char5_strlen

size_t  mulle_char5_strlen( uintptr_t value)

Retrieve the string length of value.

mulle_char5_get_maxlength

size_t  mulle_char5_get_maxlength( void)

Retrieve the maximum string length for mulle_char5_t on your system.

mulle_char5_substring

mulle_char5_t  mulle_char5_substring( mulle_char5_t value,
                                      size_t location,
                                      size_t length)

Retrieve substring of length characters of value starting at location. Range errors are ignored unless compiling with asserts enabled.

mulle_char5_is_char5string

int   mulle_char5_is_char5string( char *src, size_t len)

Check if string src of length len can be encoded as mulle_char5_t.

mulle_char5_encode

mulle_char5_t   mulle_char5_encode( char *src, size_t len)

Encode ASCII string src into len. '\0' will be ignored. When asserts are enabled, this function does some sanity checks, but it is the callers responsibility that character are 7 bit ASCII, that len is correct and that the string does not contain \0.

mulle_char5_decode

size_t  mulle_char5_decode( mulle_char5_t value, char *dst, size_t len)

Decode up to len characters of value into dst. The destination buffer must be large enough to hold len characters. Returns the actual number of characters. dst is not zero terminated!