mov_inst and add_inst procedures to avoid too much nesting

.gitignore

@@ -1,3 +1,4 @@
 /decode
 /.idea/
 /asm_files/*.bin
+/8086_family_Users_Manual_1_.pdf

asm_files/01-03-41.asm

@@ -0,0 +1,109 @@
+; ========================================================================
+; LISTING 41
+; ========================================================================
+
+bits 16
+
+add bx, [bx + si]
+add bx, [bp]
+add si, 2
+add bp, 2
+add cx, 8
+add bx, [bp + 0]
+add cx, [bx + 2]
+add bh, [bp + si + 4]
+add di, [bp + di + 6]
+add [bx + si], bx
+add [bp], bx
+add [bp + 0], bx
+add [bx + 2], cx
+add [bp + si + 4], bh
+add [bp + di + 6], di
+add byte [bx], 34
+add word [bp + si + 1000], 29
+add ax, [bp]
+add al, [bx + si]
+add ax, bx
+add al, ah
+add ax, 1000
+add al, -30
+add al, 9
+
+sub bx, [bx + si]
+sub bx, [bp]
+sub si, 2
+sub bp, 2
+sub cx, 8
+sub bx, [bp + 0]
+sub cx, [bx + 2]
+sub bh, [bp + si + 4]
+sub di, [bp + di + 6]
+sub [bx+si], bx
+sub [bp], bx
+sub [bp + 0], bx
+sub [bx + 2], cx
+sub [bp + si + 4], bh
+sub [bp + di + 6], di
+sub byte [bx], 34
+sub word [bx + di], 29
+sub ax, [bp]
+sub al, [bx + si]
+sub ax, bx
+sub al, ah
+sub ax, 1000
+sub al, -30
+sub al, 9
+
+cmp bx, [bx + si]
+cmp bx, [bp]
+cmp si, 2
+cmp bp, 2
+cmp cx, 8
+cmp bx, [bp + 0]
+cmp cx, [bx + 2]
+cmp bh, [bp + si + 4]
+cmp di, [bp + di + 6]
+cmp [bx + si], bx
+cmp [bp], bx
+cmp [bp + 0], bx
+cmp [bx + 2], cx
+cmp [bp + si + 4], bh
+cmp [bp + di + 6], di
+cmp byte [bx], 34
+cmp word [4834], 29
+cmp ax, [bp]
+cmp al, [bx + si]
+cmp ax, bx
+cmp al, ah
+cmp ax, 1000
+cmp al, -30
+cmp al, 9
+
+test_label0:
+jnz test_label1
+jnz test_label0
+test_label1:
+jnz test_label0
+jnz test_label1
+
+label:
+je label
+jl label
+jle label
+jb label
+jbe label
+jp label
+jo label
+js label
+jne label
+jnl label
+jg label
+jnb label
+ja label
+jnp label
+jno label
+jns label
+loop label
+loopz label
+loopnz label
+jcxz label

decode.c

@@ -100,30 +100,9 @@ static inline i16 get_data(unsigned char* buf, char wide)
     return wide == 1 ? (i16)buf[1] << 8 | buf[0] : (sbyte)buf[0];
 }
 
-int main(int argc, char** argv)
+bool mov_inst(FILE* f, unsigned char* buf, char inst)
 {
-    if (argc < 2)
-    {
-        printf("Usage: Please provide assembled instructions as input\n");
-        exit(0);
-    }
-    unsigned char buf[256];
-    FILE *f = fopen(argv[1], "r");
-    if (!f)
-    {
-        perror("fopen\n");
-        return EXIT_FAILURE;
-    }
-
     size_t bytes_read;
-
-    printf("; Decoded 8086 Assembly Instructions\n\n");
-    printf("bits 16\n\n");
-
-    while ((bytes_read = fread(buf, sizeof(char), 1, f)) > 0)
-    {
-        char inst = buf[0];
-        // Instruction instruction = 0;
     // Register/memory to/from register
     if ((inst & ~0x3) == (char)0b10001000)
     {
@@ -135,12 +114,10 @@ int main(int argc, char** argv)
         char mod = (next_byte & 0b11000000) >> 6;
         char reg = (next_byte & 0b00111000) >> 3;
         char rm = (next_byte & 0b00000111);
-            size_t reg_idx = reg;
-            size_t rm_idx = rm;
         if (mod == MODE_RGSTR_MODE)
         {
-                Register src_reg = d == 0 ? registers[reg_idx] : registers[rm_idx];
-                Register dst_reg = d == 0 ? registers[rm_idx] : registers[reg_idx];
+            Register src_reg = d == 0 ? registers[(size_t)reg] : registers[(size_t)rm];
+            Register dst_reg = d == 0 ? registers[(size_t)rm] : registers[(size_t)reg];
             printf("mov %s, %s ;0", reg_name(dst_reg, w), reg_name(src_reg, w));
         }
         else
@@ -158,7 +135,7 @@ int main(int argc, char** argv)
                 if (is_direct_addr) sprintf(disp_buf, "%d", abs(disp));
                 else sprintf(disp_buf, " %s %d", disp >= 0 ? "+" : "-", abs(disp));
             }
-                Register rgstr = registers[reg_idx];
+            Register rgstr = registers[(size_t)reg];
             if (d) printf("mov %s, [%s%s] ;1", reg_name(rgstr, w), eac_name, disp_buf);
             else   printf("mov [%s%s], %s ;2", eac_name, disp_buf, reg_name(rgstr, w));
         }
@@ -189,33 +166,123 @@ int main(int argc, char** argv)
         Register reg = registers[(size_t)inst & 0b00000111];
         char bytes_to_read = w == 1 ? 2 : 1;
         bytes_read = fread(buf, sizeof(char), bytes_to_read, f);
-            printf("mov %s, %hd  ;4", reg_name(reg, w), get_data(buf, w));
+        printf("mov %s, %d  ;4", reg_name(reg, w), get_data(buf, w));
     }
-        // Memory to accumulator
-        else if ((inst & ~0x1) == (char)0b10100000)
+    // Memory/accumulator to accumulator/memory
+    else if ((inst & ~0x3) == (char)0b10100000)
     {
-            printf("mov mem to acc");
+        // This instruction uses AX/AL register exclusively
+        Register ax_al = registers[0];
+        char w = (inst & 0b00000001);
+        // The manual doesn't refer to this as `d` but it acts similarly in that this bit
+        // swaps the accumulator's src/dst position
+        char d = (inst & 0b00000010) >> 1;
+        char bytes_to_read = w == 1 ? 2 : 1;
+        bytes_read = fread(buf, sizeof(char), bytes_to_read, f);
+        if (d) printf("mov [%d], %s  ;5", get_data(buf, w), reg_name(ax_al, w));
+        else   printf("mov %s, [%d]  ;6", reg_name(ax_al, w), get_data(buf, w));
     }
-        // Accumulator to memory
-        else if ((inst & ~0x1) == (char)0b10100010)
-        {
-            printf("mov acc to mem");
-        }
-        // Register/memory to segment register
-        else if (inst == (char)0b10001110)
+    // Register/memory to segment register or segment register to register/memory
+    else if ((inst & ~0x3) == (char)0b10001100)
     {
+        // Manual doesn't refer to this as `d` but swaps like in the previous instruction
+        char d = (inst & 0b00000010) >> 1;
+        (void)d;
         printf("mov regmem to segreg");
     }
-        // Segment register to register/memory
-        else if (inst == (char)0b10001100)
-        {
-            printf("mov segreg to regmem");
-        }
     else
     {
-            fprintf(stderr, "Unrecognized Instruction");
+        return false;
+    }
+    return bytes_read > 0;
 }
 
+bool add_inst(FILE* f, unsigned char* buf, char inst)
+{
+    size_t bytes_read;
+    if ((inst & ~0x3) == (char)0b00000000)
+    {
+        bytes_read = fread(buf, sizeof(char), 1, f);
+        char next_byte = buf[0];
+        char w = inst & 0b00000001;
+        char d = (inst & 0b00000010) >> 1;
+        char mod = (next_byte & 0b11000000) >> 6;
+        char reg = (next_byte & 0b00111000) >> 3;
+        char rm = (next_byte & 0b00000111);
+        // Same trick from earlier, see comment
+        int bytes_to_read = mod % 3;
+        if (bytes_to_read > 0) bytes_read = fread(buf, sizeof(char), bytes_to_read, f);
+        Register rgstr = registers[(size_t)reg];
+        (void)rm;
+        if (mod == MODE_RGSTR_MODE)
+        {
+            if (d) printf("add %s, [%d]  ;7", reg_name(rgstr, w), get_data(buf, w));
+            else   printf("add [%d], %s  ;8", get_data(buf, w), reg_name(rgstr, w));
+        }
+        else if (mod == MODE_MEM_NO_DIS)
+        {
+            if (d) printf("add %s, [%s]  ;9", reg_name(rgstr, w), get_eac_registers(rm));
+            else   printf("add [%s], %s  ;10", get_eac_registers(rm), reg_name(rgstr, w));
+        }
+        else
+        {
+            if (d) printf("add %s, [%s]  ;11", reg_name(rgstr, w), get_eac_registers(rm));
+            else   printf("add [%s], %s  ;12", get_eac_registers(rm), reg_name(rgstr, w));
+        }
+    }
+    else if ((inst & ~0x3) == (char)0b10000000)
+    {
+        bytes_read = fread(buf, sizeof(char), 1, f);
+        char w = inst & 0b00000001;
+        char mod = (buf[0] & 0b11000000) >> 6;
+        char rm = (buf[0] & 0b00000111);
+        int bytes_to_read = 1;
+        bytes_to_read += w == 0 ? 1 : 2;
+        // Same trick from earlier, see comment
+        bytes_to_read += mod % 3;
+        bytes_read = fread(buf, sizeof(char), bytes_to_read, f);
+        char *eac_name = get_eac_registers(rm);
+        i16 data = get_data(buf + (char)bytes_to_read - (w == 0 ? 1 : 2), w);
+        char *word_str = w == 0 ? "byte" : "word";
+        char disp_str[16] = {'\0'};
+        if (mod % 3 > 1) sprintf(disp_str, " + %d", get_data(buf, (mod % 3) - 1));
+        printf("add [%s%s], %s %d ;13", eac_name, disp_str, word_str, data);
+    }
+    else
+    {
+        return false;
+    }
+    return bytes_read > 0;
+}
+
+int main(int argc, char** argv)
+{
+    if (argc < 2)
+    {
+        printf("Usage: Please provide assembled instructions as input\n");
+        exit(0);
+    }
+    unsigned char buf[256];
+    FILE *f = fopen(argv[1], "r");
+    if (!f)
+    {
+        perror("fopen\n");
+        return EXIT_FAILURE;
+    }
+
+    size_t bytes_read;
+
+    printf("; Decoded 8086 Assembly Instructions\n\n");
+    printf("bits 16\n\n");
+
+    while ((bytes_read = fread(buf, sizeof(char), 1, f)) > 0)
+    {
+        char inst = buf[0];
+        if (mov_inst(f, buf, inst)) goto handled;
+        if (add_inst(f, buf, inst)) goto handled;
+
+        fprintf(stderr, "___Unrecognized Instruction___");
+    handled:
         printf("\n");
     }
 }