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Annotation of coherent/b/lib/libc/string/i8086/_memxchg.m, revision 1.1.1.1

1.1       root        1: //////////
                      2: / i8086 C string library internals.
                      3: / _memxchg()
                      4: / Exchange records of Count bytes pointed to by S1 and S2.
                      5: //////////
                      6: 
                      7: //////////
                      8: / void _memxchg(char *S1, char *S2, size_t Count)
                      9: //////////
                     10: 
                     11: #include <larges.h>
                     12: 
                     13: S1     =       LEFTARG
                     14: S2     =       S1+DPL
                     15: Count  =       S2+DPL
                     16: 
                     17:        Enter(_memxchg_)
                     18:        mov     cx, Count(bp)   / Count to CX
                     19:        jcxz    2f              / Done if Count is 0
                     20: 
                     21:        Lds     si, S2(bp)      / S2 address to DS:SI
                     22:        Les     di, S1(bp)      / S1 address to ES:DI
                     23:        cld
                     24:        shr     cx, $1          / Convert byte count to word count
                     25:        jnc     1f              / Count even, skip byte exchange
                     26: 
                     27:        movb    al, Pes (di)    / S1 byte to AL
                     28:        movsb                   / S2 byte to S1, bump DI and SI
                     29:        movb    -1(si), al      / S1 byte to old S2
                     30:        jz      2f              / Done if Count is 0
                     31: 
                     32: 1:
                     33:        mov     ax, Pes (di)    / S1 word to AX
                     34:        movs                    / S2 word to S1, bump DI and SI
                     35:        mov     -2(si), ax      / S1 word to old S2
                     36:        loop    1b              / Decrement byte count and repeat
                     37: 
                     38: 2:
                     39:        Leave

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