From 2f6a51855571ee12bad247ac026aa02a061800f0 Mon Sep 17 00:00:00 2001
From: Charles Cabergs <me@cacharle.xyz>
Date: Tue, 16 Nov 2021 18:42:30 +0100
Subject: Updated to generate correct assembly (segfaults)

---
 bfc.c                       | 71 +++++++++++++++++++++++++++++++++------------
 examples/add_2_5.bf         | 20 +++++++++++++
 examples/getchar_putchar.bf |  1 +
 3 files changed, 74 insertions(+), 18 deletions(-)
 create mode 100644 examples/add_2_5.bf
 create mode 100644 examples/getchar_putchar.bf

diff --git a/bfc.c b/bfc.c
index cb1b0f9..2d4c8f9 100644
--- a/bfc.c
+++ b/bfc.c
@@ -2,52 +2,87 @@
 #include <stdlib.h>
 #include <stdio.h>
 
-const size_t buffer_size = 256;
-const char* asm_filename = "out.asm";
+static const size_t buffer_size = 256;
+static const char* asm_filename = "out.asm";
+
+static const char *write_syscall = "0x2000004";
+static const char *read_syscall  = "0x2000003";
+
+#define LABEL_COUNT_STACK_SIZE 256
+static size_t label_stack[LABEL_COUNT_STACK_SIZE + 1] = {0};
+static size_t label_stack_frame = 0;
 
 int main(int argc, char *argv[])
 {
-    FILE* file = fopen(asm_filename, "w");
+    FILE *input_file = NULL;
+    if (argc == 2)
+        input_file = fopen(argv[1], "r");
+    else
+        input_file = stdin;
+
+    /* FILE* output_file = fopen(asm_filename, "w"); */
+    FILE *output_file = stdout;
     fprintf(
-        file,
+        output_file,
+        "global _start\n"
         "section .bss\n"
-        "buffer: resb %zu\n"
-        "section .text\n",
-        "mov rax buffer\n",
+        "\tbuffer: resb %zu\n\n"
+        "section .text\n"
+        "_start:\n"
+        "\tmov rbx, buffer\n",
         buffer_size
     );
+    size_t label_frame_id;
 
     char c;
-    while ((c = fgetc(file)) != EOF)
+    while ((c = fgetc(input_file)) != EOF)
     {
         switch (c)
         {
         case '>':
-            fputs("inc rax");
+            fprintf(output_file, "    inc rbx              ; >\n");
             break;
         case '<':
-            fputs("dec rax");
+            fprintf(output_file, "    dec rbx              ; <\n");
             break;
         case '+':
-            fputs("inc [rax]");
+            fprintf(output_file, "    inc byte [rbx]       ; +\n");
             break;
         case '-':
-            fputs("dec [rax]");
+            fprintf(output_file, "    dec byte [rbx]       ; -\n");
             break;
         case '.':
-            // putchar 
+            fprintf(output_file, "    mov rdi, 1           ; .\n");
+            fprintf(output_file, "    mov rsi, rbx         ; .\n");
+            fprintf(output_file, "    mov rdx, 1           ; .\n");
+            fprintf(output_file, "    mov rax, %-10s  ; .\n", write_syscall);
+            fprintf(output_file, "    syscall              ; .\n");
             break;
         case ',':
-            // getchar
+            fprintf(output_file, "    mov rdi, 0           ; ,\n");
+            fprintf(output_file, "    mov rsi, rbx         ; ,\n");
+            fprintf(output_file, "    mov rdx, 1           ; ,\n");
+            fprintf(output_file, "    mov rax, %-10s  ; ,\n", read_syscall);
+            fprintf(output_file, "    syscall              ; ,\n");
             break;
         case '[':
-            // jump to next ] if byte at data ptr is 0
+            label_frame_id = label_stack[label_stack_frame];
+            fprintf(output_file, "label_open_%03d_%03d:          ; [\n", label_stack_frame, label_frame_id);
+            fprintf(output_file, "    cmp byte [rbx], 0    ; [\n");
+            fprintf(output_file, "    je  label_close_%03d_%03d  ; [\n", label_stack_frame, label_frame_id);
+            label_stack_frame++;
             break;
-        case '[':
-            // jump to prev [ if byte at data ptr is not 0
+        case ']':
+            label_stack_frame--;
+            label_frame_id = label_stack[label_stack_frame];
+            fprintf(output_file, "label_close_%03d_%03d:         ; ]\n", label_stack_frame, label_frame_id);
+            fprintf(output_file, "    cmp byte [rbx], 0    ; ]\n");
+            fprintf(output_file, "    jne label_open_%03d_%03d   ; ]\n", label_stack_frame, label_frame_id);
+            label_stack[label_stack_frame]++;
             break;
         case ';':
-            // comment
+            while (c != EOF && c != '\n')
+                c = fgetc(input_file);
             break;
         default:
             // error
diff --git a/examples/add_2_5.bf b/examples/add_2_5.bf
new file mode 100644
index 0000000..a6425d7
--- /dev/null
+++ b/examples/add_2_5.bf
@@ -0,0 +1,20 @@
+++       ; Cell c0 = 2
+> +++++  ; Cell c1 = 5
+
+[        ; Start your loops with your cell pointer on the loop counter (c1 in our case)
+< +      ; Add 1 to c0
+> -      ; Subtract 1 from c1
+]        ; End your loops with the cell pointer on the loop counter
+
+; At this point our program has added 5 to 2 leaving 7 in c0 and 0 in c1
+; but we cannot output this value to the terminal since it is not ASCII encoded.
+
+; To display the ASCII character "7" we must add 48 to the value 7.
+; We use a loop to compute 48 = 6 * 8.
+
+++++ ++++  ; c1 = 8 and this will be our loop counter again
+[
+< +++ +++  ; Add 6 to c0
+> -        ; Subtract 1 from c1
+]
+< .        ; Print out c0 which has the value 55 which translates to "7"!
diff --git a/examples/getchar_putchar.bf b/examples/getchar_putchar.bf
new file mode 100644
index 0000000..f36f02a
--- /dev/null
+++ b/examples/getchar_putchar.bf
@@ -0,0 +1 @@
+,.
-- 
cgit