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INCHKSUM.ASM
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Upload User: sunrenlu
Upload Date: 2022-06-13
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Code Size: 1k
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OS Develop

Development Platform:

DOS

INCHKSUM.ASM：Code Content
  1. ;
  2. ;
  3. ;  Usage :
  4. ;           void far *inchksum()
  5. ;
  6. ;  Internet compatible 1's complement checksum
  7. ;
  8. ;  (c) 1990 Erick Engelke
  9. ;
  10. ;  version
  11. ;
  12. ;    0.1    17 Dec -1990   E. P. Engelke
  13. ;
  14. ;
  15.         include masmdefs.hsm
  16.         include model.hsm
  18. codedef INCHKSUM
  19. datadef
  21. cstart  INCHKSUM
  22. cpublic inchksum
  23.         ; Compute 1's-complement sum of data buffer
  24.         ;
  25.         ; unsigned lcsum( usigned far *buf, unsigned cnt)
  26. push DS
  27.         lds     SI, +@AB + 0 [BP]
  28. mov     CX, +@AB + 4 [BP]       ; cx = cnt
  30.         mov     BL, CL
  32. shr     CX, 1 ; group into words
  33. xor DX, DX ; set checksum to 0
  34.         cld
  36.         jcxz    remain
  37.         clc
  38. deloop: lodsw
  39. adc DX, AX
  40. loop deloop
  42.         adc     DX, 0                   ; only two necessary
  43.         adc     DX, 0
  45. remain: and     BL, 1
  46.         jz      done
  48.         xor     AH, AH
  49.         lodsb
  50.         add     DX, AX
  51.         adc     DX, 0
  52.         adc     DX, 0
  54. done:   mov AX,DX ; result into ax
  55.         or      AX,AX
  56. ok:     pop     DS
  57. creturn inchksum
  58. cend    INCHKSUM
  59.         end