Memcmp.asm

Functions Provided

Entry point	Function provided	Notes
MEMCMP	Compare two blocks of memory	First source, second source and length fixed in ROM.
MEMCMP.1		First source, second source and length in registers.

See source code below for calling convention.

Examples

(todo... please contribute!)

Source Code

;* ======================================================================== *;
;*  These routines are placed into the public domain by their author.  All  *;
;*  copyright rights are hereby relinquished on the routines and data in    *;
;*  this file.  -- Joseph Zbiciak, 2008                                     *;
;* ======================================================================== *;

;; ======================================================================== ;;
;;  MEMCMP    Compare Two Arrays                                            ;;
;;  MEMCMP.1  Alternate entry point                                         ;;
;;                                                                          ;;
;;  AUTHOR                                                                  ;;
;;      Joseph Zbiciak <intvnut AT gmail.com>                               ;;
;;                                                                          ;;
;;  REVISION HISTORY                                                        ;;
;;      08-Sep-2001 Initial Revision                                        ;;
;;                                                                          ;;
;;  INPUTS for MEMCMP                                                       ;;
;;      R5    Pointer to invocation record, followed by return address.     ;;
;;            Pointer to first array       1 DECLE                          ;;
;;            Pointer to second array      1 DECLE                          ;;
;;            Length                       1 DECLE                          ;;
;;                                                                          ;;
;;  INPUTS for MEMCMP.1                                                     ;;
;;      R5    Return address                                                ;;
;;      R4    Pointer to first array                                        ;;
;;      R1    Pointer to second array                                       ;;
;;      R0    Length                                                        ;;
;;                                                                          ;;
;;  OUTPUTS                                                                 ;;
;;      R0    Zero if all elements compared as equal, non-zero otherwise.   ;;
;;      R1    Last element compared against from first array.               ;;
;;      R4    If miscompared, points just after miscompare in 1st array,    ;;
;;            otherwise points to first element beyond end of array.        ;;
;;      R5    If miscompared, points just after miscompare in 2nd array,    ;;
;;            otherwise points to first element beyond end of array.        ;;
;;      FLAGS Result of comparison between the arrays.                      ;;
;;                                                                          ;;
;;  TECHNIQUES                                                              ;;
;;      Unrolled 2x for speed.                                              ;;
;;                                                                          ;;
;;  CODESIZE                                                                ;;
;;      23 words                                                            ;;
;;                                                                          ;;
;;  CYCLES                                                                  ;;
;;      If length is even:  cycles =  74 + 61*floor(length / 2)             ;;
;;      If length is odd:   cycles = 107 + 61*floor(length / 2)             ;;
;;                                                                          ;;
;;      If calling MEMCMP.1, subtract 24 cycles from the above formulae.    ;;
;; ======================================================================== ;;
MEMCMP      PROC

            MVI@    R5,     R4      ;   8   First array
            MVI@    R5,     R1      ;   8   Second array
            MVI@    R5,     R0      ;   8   Length

@@1:        PSHR    R5              ;   9   Alternate entry point

            MOVR    R1,     R5      ;   6   Use auto-incr pointer

            INCR    R0              ;   6   \    Loop is unrolled 2x, so 
            SARC    R0,     1       ;   6    |-- handle the odd iteration.
            BNC     @@odd           ;  7/9  /   
            BEQ     @@done          ;  7/9  Abort if length == 0.
                                    ;---- 
                                    ;  65   Fallthru case
                                    ;  60   Branch to odd

@@loop:     MVI@    R5,     R1      ;   8   \
            CMP@    R4,     R1      ;   8    |-- Compare one pair of words
            BNEQ    @@done          ;  7/9  /
            
@@odd:      MVI@    R5,     R1      ;   8   \
            CMP@    R4,     R1      ;   8    |-- Compare one pair of words
            BNEQ    @@done          ;  7/9  /
            
            DECR    R0              ;   6   
            BNEQ    @@loop          ;  9/7  Iterate
                                    ;----
                                    ;  61*k - 2

@@done:     PULR    PC              ;  11   Return, w/ result in FLAGS.
            ENDP    


;; ======================================================================== ;;
;;  End of File:  memcmp.asm                                                ;;
;; ======================================================================== ;;