path: root/zap/source/amd64/mem/memfor.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_memfor

zap_memfor:
# Address of the current element:
#define addr     %rbx
# Address of the element after the last input element:
#define afterbuf %r12
# Size of each input element:
#define sz       %r13
# Address of the function:
#define fn       %r14

	# 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 addr
	pushq afterbuf
	pushq sz
	pushq fn

	# Move registers into place:
	movq %rdi,addr
	movq %rsi,sz
	movq %rdx,afterbuf
	movq %rcx,fn

	# Get the one-past-the-end address:
	imulq sz,afterbuf  # afterbuf *= sz   // 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 addr,afterbuf # afterbuf += addr

	# Iterate through the array:
.loop:

	# Check if we have reached the one-past-the-end address:
	cmpq addr,afterbuf # if (addr == afterbuf)
	je .done           # goto done

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

	# Continue to the next element:
	addq sz,addr # addr += sz
	jmp .loop    # goto loop

	# Finish:
.done:
	
	# Restore the callee-saved registers:
	popq fn
	popq sz
	popq afterbuf
	popq addr

	ret # return