; Turbo Assembler    Copyright (c) 1988, 1991 By Borland International, Inc.

; EXCHMOD.ASM

; From the Turbo Assembler Users Guide

          .MODEL  large,PASCAL
          .CODE
Exchange  PROC FAR var1:DWORD,var2:DWORD,count:WORD
          PUBLIC Exchange;
          cld                  ;exchange goes upward
          mov     dx,ds        ;save DS
          lds     si,var1      ;get first address
          les     di,var2      ;get second address
          mov     cx,count     ;get number of bytes to move
          shr     cx,1         ;get word count (low bit -> carry)
          jnc     ExchangeWords  ;if no odd byte, enter loop
          mov     al,es:[di]     ;read odd byte from var2
          movsb                  ;move a byte from var1 to var2
          mov     [si-1],al      ;write var2 byte to var1
          jz      Finis          ;done if only 1 byte to exchange
ExchangeWords:
          mov     bx,-2          ;BX is a handy place to keep -2
ExchangeLoop:
          mov     ax,es:[di]     ;read a word from var2
          movsw                  ;do a move from var1 to var2
          mov     [bx][si],ax    ;write var2 word to var1
          loop    ExchangeLoop   ;repeat "count div 2" times
Finis:
          mov     ds,dx          ;get back Turbo's DS
          ret
Exchange  ENDP
          END
