Memunpk.asm

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Contents

Functions Provided

Entry pointFunction providedNotes
MEMUNPKLike memcpy.asm, but unpacks 8-bit data stored in 16-bit wordsSource, destination and length fixed in ROM.
MEMUNPK.1Source, destination and length in registers.



See source code below for calling convention.

Examples

(todo... please contribute!)

Notes

The code expects to write the data in 8-bit memory, such as Scratchpad RAM or Graphics RAM, and so does not explicitly mask the written value. Instead, it relies on the hardware ignoring the upper 8 bits of the write. This works as expected when writing to 8-bit RAM, which is its intended use.

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                                     *;
;* ======================================================================== *;

;; ======================================================================== ;;
;;  MEMUNPK   Unpack a 16-bit array to an 8-bit array.                      ;;
;;  MEMUNPK.1 Alternate entry point                                         ;;
;;                                                                          ;;
;;  AUTHOR                                                                  ;;
;;      Joseph Zbiciak <intvnut AT gmail.com>                               ;;
;;                                                                          ;;
;;  REVISION HISTORY                                                        ;;
;;      08-Sep-2001 Initial Revision                                        ;;
;;                                                                          ;;
;;  INPUTS for MEMUNPK                                                      ;;
;;      R5    Pointer to invocation record, followed by return address.     ;;
;;            Pointer to destination       1 DECLE                          ;;
;;            Pointer to source            1 DECLE                          ;;
;;            Length of source array       1 DECLE                          ;;
;;                                                                          ;;
;;  INPUTS for MEMUNPK.1                                                    ;;
;;      R5    Return address                                                ;;
;;      R4    Pointer to destination                                        ;;
;;      R1    Pointer to source                                             ;;
;;      R0    Length of source array                                        ;;
;;                                                                          ;;
;;  OUTPUTS                                                                 ;;
;;      R0    $FFFF                                                         ;;
;;      R1    Last 16-bit word copied, byte-swapped.                        ;;
;;      R4    Points one element beyond destination array                   ;;
;;      R5    Points one element beyond source array                        ;;
;;                                                                          ;;
;;  TECHNIQUES                                                              ;;
;;      Unrolled 4x for speed.                                              ;;
;;      Special dispatch handles length % 4 != 0.                           ;;
;;                                                                          ;;
;;  CODESIZE                                                                ;;
;;      ?? words                                                            ;;
;;                                                                          ;;
;;  CYCLES                                                                  ;;
;;      Not yet characterized.                                              ;;
;; ======================================================================== ;;
MEMUNPK     PROC

            MVI@    R5,     R4      ;   8   Destination array
            MVI@    R5,     R1      ;   8   Source array
            MVI@    R5,     R0      ;   8   Length

@@1:        PSHR    R5              ;   9   Alternate entry point

            MOVR    R1,     R5      ;   6   Use auto-incr pointer

            MOVR    R0,     R1      ;   6   Copy array length
            SLR     R0,     2       ;   8   Find floor(length / 4)
            ANDI    #3,     R1      ;   8   \
            SLL     R1,     2       ;   8    |__ Find address to jump to for
            SUBI    #@@end, R1      ;   8    |   first iteration, to handle
            NEGR    R1              ;   6   /    length % 4.
            MOVR    R1,     PC      ;   6   Jump into copy loop.

@@loop:     MVI@    R5,     R1      ;   8   \
            MVO@    R1,     R4      ;   9    |__ Copy first pair of bytes
            SWAP    R1,     1       ;   6    |
            MVO@    R1,     R4      ;   9   /
            MVI@    R5,     R1      ;   8   \
            MVO@    R1,     R4      ;   9    |__ Copy second pair of bytes
            SWAP    R1,     1       ;   6    |
            MVO@    R1,     R4      ;   9   /
            MVI@    R5,     R1      ;   8   \
            MVO@    R1,     R4      ;   9    |__ Copy third pair of bytes
            SWAP    R1,     1       ;   6    |
            MVO@    R1,     R4      ;   9   /
            MVI@    R5,     R1      ;   8   \
            MVO@    R1,     R4      ;   9    |__ Copy fourth pair of bytes
            SWAP    R1,     1       ;   6    |
            MVO@    R1,     R4      ;   9   /
            
@@end:      DECR    R0              ;   6   
            BPL     @@loop          ;  9/7  Iterate floor(length/4) + 1 times
                                    ;----
                                    ; 143*k - 2

@@done:     PULR    PC              ;  11   Return
            ENDP    


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