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⌂ ∞ Elite on the BBC Micro and NES

Drawing the screen: FILL_MEMORY

[NES version, Common]

       Name: FILL_MEMORY                                             [Show more]
       Type: Macro
   Category: Drawing the screen
    Summary: Fill memory with the specified number of bytes

    Context: See this macro in context in the source code
 References: This macro is used as follows:
             * ClearMemory uses FILL_MEMORY
             * FillMemory uses FILL_MEMORY
             * FillMemory32Bytes uses FILL_MEMORY




 The following macro is used to fill a block of memory with the same value:

   FILL_MEMORY byte_count

 It writes the value A into byte_count bytes, starting at the Y-th byte of the
 memory block at address clearAddress(1 0). It also updates the index in Y to
 point to the byte after the block that is filled.



 Arguments:

   byte_count           The number of bytes to fill

   clearAddress(1 0)    The base address of the block of memory to fill

   Y                    The index into clearAddress(1 0) from which to fill

   A                    The value to fill



 Returns:

   Y                    The index in Y is updated to point to the byte after the
                        filled block



MACRO FILL_MEMORY byte_count

 FOR I%, 1, byte_count

  STA (clearAddress),Y  ; Write A to the Y-th byte of clearAddress(1 0)

  INY                   ; Increment the index in Y

                        ; Repeat the above code so that we run it byte_count
                        ; times, so write a total of byte_count bytes into
                        ; memory

 NEXT

ENDMACRO