Synopsis #

Header: fxcg/system.h
Syscall index: 0x1163
Function signature: int MB_ElementCount(const char* buf)

Counts the number of characters, as printed on screen, of a multi-byte string.

Parameters #

• buf - pointer to the string to measure.

Returns #

The number of characters in the string, as printed by multi-byte-aware syscalls.

Comments #

Here is a disassembly of the function.

! =============== S U B    R O U T I N E =======================================


MB_ElementCount:
        tst r4, r4      ! Is r4 NULL?
        bt  MB_ElementCount_exit ! If yes, branch.
        mov #0xFFFFFFE5, r1
        mov #0xFFFFFFE6, r7
        extu.b  r1, r1      ! r1=229
        mov #0, r5
        bra loc_801A3478
        extu.b  r7, r7      ! r7=230
! ---------------------------------------------------------------------------

MB_ElementCount_charLoop:
        cmp/eq  #0x7F, r0
        bt  loc_801A3472
        cmp/eq  r1, r0
        bt  loc_801A3472
        cmp/eq  r7, r0
        bt  loc_801A3472
        mov #0xFFFFFFE7, r2
        extu.b  r2, r2
        cmp/eq  r2, r0
        bt  loc_801A3472
        mov #0xFFFFFFF7, r2
        extu.b  r2, r2
        cmp/eq  r2, r0
        bt  loc_801A3472
        mov #0xFFFFFFF9, r2
        extu.b  r2, r2
        cmp/eq  r2, r0
        bf  loc_801A3474

loc_801A3472:
        add #1, r4

loc_801A3474:
        add #1, r4
        add #1, r5

loc_801A3478:
        mov.b   @r4, r2
        extu.b  r2, r0
        tst r0, r0
        bf  MB_ElementCount_charLoop ! Branch if the character has a non-zero value.
        rts
        mov r5, r0
! ---------------------------------------------------------------------------

MB_ElementCount_exit:
        rts
        mov #0, r0
! End of function MB_ElementCount

Example #

The following example shows how a multi-byte string can take a memory space that’s twice as large as the number of printed characters, and demonstrates how to count both size in bytes and graphical size:

const char*MBstring="\xe6\x92\xe6\x93\xe6\xa5"
int bytelen = strlen(MBstring);
// bytelen has a value of 6
int elemlen = MB_ElementCount(MBstring);
// elemlen has a value of 3

locate_OS(2,3);
Print_OS(MBstring, 0, 0); // will print three symbols on screen: an arrow up, an arrow down and a square.

Another example, which mixes standard and multi-byte characters:

const char*MBstring="Empty box: \xe6\xa5";
int bytelen = strlen(MBstring);
// bytelen has a value of 13
int elemlen = MB_ElementCount(MBstring);
// elemlen has a value of 12

locate_OS(2,3);
Print_OS(MBstring, 0, 0); // will print "Empty box: " followed by a square.