path: root/zap/source/amd64/mem/foreach.S

# Copyright 2022 Gabriel Jensen.
# This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
# If a copy of the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.

.globl zap_foreach

zap_foreach:
	# rbx: Address of the current element.
	# r12: Address of the element after the last input element.
	# r13: Size of each input element.
	# r14: Address of the function.

	# We're gonna use callee-saved registers for storing values so they don't get overwritten with each function call.

	# Push the callee-saved registers:
	pushq %rbx
	pushq %r12
	pushq %r13
	pushq %r14

	# Move registers into place:
	movq %rdi,%rbx
	movq %rsi,%r13
	movq %rcx,%r14

	# Get the one-past-the-end address:
	movq %rdx,%r12
	imulq %r13,%r12 # Calculate the array size in bytes (sz * num). We're using signed multiply because the equivalent using the unsigned instruction would use more instructions.
	addq %rbx,%r12

	# Iterate through the array:
.loop:

	# Check if we have reached the one-past-the-end address:
	cmpq %rbx,%r12
	je .done

	# Call the provided function:
	movq %rbx,%rdi # Provide the current address to the function.
	call *%r14 # We don't need to save any registers for this as we only use callee-saved registers.

	# Continue to the next element:
	addq %r13,%rbx
	jmp .loop

	# Finish:
.done:
	
	# Restore the callee-saved registers:
	popq %r14
	popq %r13
	popq %r12
	popq %rbx

	ret