// #LAYOUT# STD *       #TAKE
// #LAYOUT# *   BASIC_0 #TAKE
// #LAYOUT# *   *       #IGNORE


//
// Copies the memory down
//
// Input:
// - memmove__src  - pointer to the first byte of source
// - memmove__dst  - pointer to the first byte of destination
// - memmove__size - number of bytes to copy
//
// All the input variables, .A, and .Y register, are destroyed. Also uses memmove__tmp variable.
//


shift_mem_down:

	// The copy routine is simplified, so that it is fast and (for memory model 60K)
	// can fit in a small RAM area - therefore it requires to pre-set .Y, so that
	// the copy ends when it reaches 0; so if copying one byte we want .Y = $FF

	sec
	lda #$00
	sbc memmove__size+0
	tay

	// Now we have to move down the memmove_src and memmove_dst pointers to compensate for .Y not being 0

	jsr shift_mem_adapt_pointers

#if CONFIG_MEMORY_MODEL_38K

shift_mem_down_internal:

	// Move memmove__size bytes from memmove__src to memmove__dst, where memmove__dst > memmove__src
	//
	// This means we have to copy from the back end down.
	// This routine assumes the pointers are already pointed to the end of the areas, and that .Y is correctly initialized

	php
!:
	lda (memmove__src),y
	sta (memmove__dst),y
	iny
	bne !-
	inc memmove__src+1
	inc memmove__dst+1
	dec memmove__size+1
	bne !-
	plp
	rts

#else

	jmp shift_mem_down_internal

#endif