1 files changed, 59 insertions, 0 deletions
diff --git a/zap/source/amd64/mem/memfor.S b/zap/source/amd64/mem/memfor.S
new file mode 100644
index 0000000..be705b9
--- /dev/null
+++ b/zap/source/amd64/mem/memfor.S
@@ -0,0 +1,59 @@
+# 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 %rcx,fn
+
+	# Get the one-past-the-end address:
+	movq %rdx,afterbuf
+	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