Added support for MOVSX (#32)

This pull has added complete support for the MOVSX (Move with sign
extension) instruction, since this instruction exhibits very similar
encodings to the previously implemented MOVSX instruction, many encoding
functionality and encoder tables can be *shared* (Such as pre-processors
and opcods)

Although this pull is listed as only adding support for the MOVSX
instruction, this pull has also renamed the `pre_movzx` pre-proces-
or function `pre_small_operands` to better encapsulate its behavior
and allowing cross-usage to other instruction enocder tables.

TODO.txt

@@ -31,7 +31,7 @@ https://docs.google.com/document/d/1bm9lxVyAk2qogOF9ujERyRcSwXkpKxLW8IWVU8FuMyE/
 More instructions:
 Data Movement Instructions
 XCHG: Exchange data between registers or memory.
-MOVSX/MOVZX: Move with sign/zero extension.
+MOVSX/MOVZX: Move with sign/zero extension. - ✅
 BSWAP: Byte swap (useful for endian conversion).
 CMOVcc: Conditional move based on flags (e.g., CMOVZ, CMOVNZ).
 Arithmetic and Logic Instructions

libjas/include/instruction.h

@@ -83,6 +83,7 @@ enum instructions {
   INSTR_INT,
   INSTR_SYSCALL,
   INSTR_MOVZX,
+  INSTR_MOVSX,
 
   INSTR_DUMMY,
 

libjas/instruction.c

@@ -176,12 +176,13 @@ DEFINE_TAB(syscall) = {
     INSTR_TERMINATOR,
 };
 
-static void pre_movzx(operand_t *op_arr, buffer_t *buf, instr_encode_table_t *instr_ref, enum modes mode) {
+static void pre_small_operands(operand_t *op_arr, buffer_t *buf, instr_encode_table_t *instr_ref, enum modes mode) {
   if (op_sizeof(op_arr[1].type) < 16)
     err("Invalid operand size for MOVZX instruction");
 }
 
-DEFINE_TAB(movzx) = {{ENC_RM, NULL, {0x0F, 0xB7}, MODE_SUPPORT_ALL, {0x0F, 0xB6}, 2, &pre_movzx, true}, INSTR_TERMINATOR};
+DEFINE_TAB(movzx) = {{ENC_RM, NULL, {0x0F, 0xB7}, MODE_SUPPORT_ALL, {0x0F, 0xB6}, 2, &pre_small_operands, true}, INSTR_TERMINATOR};
+DEFINE_TAB(movsx) = {{ENC_RM, NULL, {0x0F, 0xBF}, MODE_SUPPORT_ALL, {0x0F, 0xBE}, 2, &pre_small_operands, true}, INSTR_TERMINATOR};
 
 // clang-format off
 
@@ -190,7 +191,7 @@ instr_encode_table_t *instr_table[] =
         mov, lea, add, sub, mul, div, and, or, xor, _not, inc,
         dec, jmp, je, jne, jz, jnz, call, ret, cmp, push, pop,
         in, out, clc, stc, cli, sti, nop, hlt, _int, syscall, 
-        movzx,
+        movzx, movsx,
     };