From 5fe5b58147198747f5f33d9142b46f54f34cd3ad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Wed, 12 May 2021 17:36:43 +0300
Subject: [PATCH] Minimize size further and fix bug where . used stdin instead
 of stdout

---
 minibfc.asm | 84 +++++++++++++++++++++++++++++------------------------
 1 file changed, 46 insertions(+), 38 deletions(-)

diff --git a/minibfc.asm b/minibfc.asm
index 9c3c400..f9c0d81 100644
--- a/minibfc.asm
+++ b/minibfc.asm
@@ -46,49 +46,50 @@ _start:
 	mov rdi, rsp
 
 	.copy_header:
-		mov rsi, $$
-		mov rcx, headers_length
+		mov esi, $$
+		mov ecx, headers_length
 		rep movsb
 
 	.copy_init:
-		mov rsi, init_code
-		mov rcx, init_code_length
+		mov esi, init_code
+		mov ecx, init_code_length
 		rep movsb
 
 	mov rbp, rdi
 
 mainloop:
 	; Read one byte
-	mov rax, 0
-	mov rdi, 0
+	xor eax, eax
+	xor edi, edi
 	mov rsi, rbp
-	mov rdx, 1
+	xor edx, edx
+	inc edx
 	syscall
 
 	.was_eof:
-		test rax, rax
+		test eax, eax
 		jz end
 
 	mov al, [rbp]
 
-	mov rcx, 8
-	mov rbx, command_table
-	xor rdx, rdx
+	mov ecx, 8
+	mov ebx, command_table
+	xor edx, edx
 
 	.table_find:
-		mov dl, [rbx+1]
-		cmp al, [rbx]
+		mov dl, [ebx+1]
+		cmp al, [ebx]
 		je .table_found
 		add dl, 2
-		add rbx, rdx
+		add ebx, edx
 		loop .table_find
-		xor rdx, rdx
+		xor edx, edx
 
 		.table_found:
-			lea rsi, [rbx + 2]
+			lea esi, [ebx + 2]
 
 	mov rdi, rbp
-	mov rcx, rdx
+	mov ecx, edx
 	rep movsb
 	mov rbp, rdi
 
@@ -96,9 +97,9 @@ mainloop:
 
 end:
 	.copy_end_code:
-		mov rsi, end_code
+		mov esi, end_code
 		mov rdi, rbp
-		mov rcx, end_code_length
+		mov ecx, end_code_length
 		rep movsb
 		mov rbp, rdi
 
@@ -143,10 +144,10 @@ end:
 			stosd
 
 			; Jumping backwards, we need to invert the displacement and then account for the size of the [
-			neg rax
-			xor rbx, rbx
+			neg eax
+			xor ebx, ebx
 			mov byte bl, [while_length]
-			sub rax, rbx
+			sub eax, ebx
 
 			; Store in our displacement field
 			mov rdi, rsi
@@ -159,24 +160,25 @@ end:
 
 		.fixup_done:
 
-	xor rbx, rbx
+	xor ebx, ebx
 	.output_loop:
 		mov rsi, rsp
 		add rsi, rbx
 		cmp rsi, rbp
 
 		je .exit
-		mov rax, 1
-		mov rdi, 1
-		mov rdx, 1
+		xor eax, eax
+		inc eax
+		mov edi, eax
+		mov edx, eax
 		syscall
 
-		inc rbx
+		inc ebx
 		jmp .output_loop
 
 	.exit:
-		mov rax, 60
-		xor rdi, rdi
+		mov eax, 60
+		xor edi, edi
 		syscall
 
 command_table:
@@ -204,32 +206,38 @@ command_table:
 		times 3 db 0
 	getc: db ',', putc - $ - 2
 		mov byte [rbx], 0
-		mov rax, 0
-		mov rdi, 0
+		xor eax, eax
+		xor edi, edi
 		mov rsi, rbx
-		mov rdx, 1
+		xor edx, edx
+		inc edx
 		syscall
 	putc: db '.', ._end - $ - 2
-		mov rax, 1
-		mov rdi, 0
+		xor eax, eax
+		inc eax
+		mov edi, eax
 		mov rsi, rbx
-		mov rdx, 1
+		mov edx, eax
 		syscall
 	._end:
 
 init_code:
-	mov rcx, 0x10000 ; 64KiB of memory
+	mov ecx, 0x10000 ; 64KiB of memory
+
+	; Clear out the memory
 	sub rsp, rcx
 	mov rdi, rsp
-	mov rbx, rdi
 	xor al, al
 	rep stosb
 
+	; Initialize tape head
+	mov rbx, rsp
+
 	init_code_length equ $ - init_code
 
 end_code:
 	mov rax, 60
-	xor rdi, rdi
+	xor edi, edi
 	syscall
 
 	end_code_length equ $ - end_code