From d7583bf11c618d2e1ee4a89d9d9f394172489aa8 Mon Sep 17 00:00:00 2001
From: ladevieq <ladevie.quentin@gmail.com>
Date: Sat, 25 Jul 2026 22:56:08 +0200
Subject: Fix REX prefix detection Improve relative offset printing

---
 src/disasm.c | 38 +++++++++++++++++++++++++++++---------
 src/utils.c  |  2 +-
 2 files changed, 30 insertions(+), 10 deletions(-)

(limited to 'src')

diff --git a/src/disasm.c b/src/disasm.c
index 36df605..4671611 100644
--- a/src/disasm.c
+++ b/src/disasm.c
@@ -1041,7 +1041,7 @@ void unassemble(u8* start, u64 size) {
         UNUSED_VAR(ModRM_RM_extended);
         u8 SIB_index_extended = 0U;
         UNUSED_VAR(SIB_index_extended);
-        if ((has_REX_prefix = ((*current_byte & REX_prefix_mask) == REX_prefix_mask)) == TRUE) {
+        if ((has_REX_prefix = ((*current_byte & 0b11000000) == REX_prefix_mask)) == TRUE) {
             u8 REX = *current_byte;
             current_byte++;
 
@@ -1184,7 +1184,11 @@ void unassemble(u8* start, u64 size) {
                     if (Mod == 0b11) { // Register direct addressing mode
                         print(" %s", get_ModRM_reg(RM, effective_operand_size, use_3DNow_reg, use_SSE_reg));
                     } else if (RM == 0b101) {
-                        print(" RIP + %d", disp);
+                        if (disp < 0) {
+                            print(" [RIP - 0x%x]", -disp);
+                        } else {
+                            print(" [RIP + 0x%x]", disp);
+                        }
                     } else if(RM != 0b100) { // Register indirect addressing mode
                         print(" %s", get_ModRM_reg(RM, effective_operand_size, use_3DNow_reg, use_SSE_reg));
                     }
@@ -1197,7 +1201,11 @@ void unassemble(u8* start, u64 size) {
                     print(" 0x%x", src_imm);
                     break;
                 case TYPE_J:
-                    print(" RIP + %d", rel_offset);
+                    if (rel_offset < 0) {
+                        print(" [RIP - 0x%x]", -rel_offset);
+                    } else {
+                        print(" [RIP + 0x%x]", rel_offset);
+                    }
                     break;
                 case Reg:
                     print(" %s", registers[op->src_operand.reg]);
@@ -1225,11 +1233,13 @@ void unassemble(u8* start, u64 size) {
                     if (index != 0b100) {
                         print(" +");
                     }
-                    print(" [base(%s)]", SIB_base_registers[base]);
+                    print(" [base(%s)", SIB_base_registers[base]);
                 }
 
                 if (disp_bytes_count) {
-                    print(" + offset(0x%x)", disp);
+                    print(" + offset(0x%x)]", disp);
+                } else {
+                    print("]");
                 }
             }
         }
@@ -1250,7 +1260,11 @@ void unassemble(u8* start, u64 size) {
                     if (Mod == 0b11) { // Register direct addressing mode
                         print(" %s", get_ModRM_reg(RM, effective_operand_size, use_3DNow_reg, use_SSE_reg));
                     } else if (RM == 0b101) {
-                        print(" RIP + %d", disp);
+                        if (disp < 0) {
+                            print(" [RIP - 0x%x]", -disp);
+                        } else {
+                            print(" [RIP + 0x%x]", disp);
+                        }
                     } else if(RM != 0b100) { // Register indirect addressing mode
                         print(" %s", get_ModRM_reg(RM, effective_operand_size, use_3DNow_reg, use_SSE_reg));
                     }
@@ -1263,7 +1277,11 @@ void unassemble(u8* start, u64 size) {
                     print(" 0x%x", dst_imm);
                     break;
                 case TYPE_J:
-                    print("RIP + %d", rel_offset);
+                    if (rel_offset < 0) {
+                        print(" [RIP - 0x%x]", -rel_offset);
+                    } else {
+                        print(" [RIP + 0x%x]", rel_offset);
+                    }
                     break;
                 case Reg:
                     print(" %s", registers[op->src_operand.reg]);
@@ -1291,11 +1309,13 @@ void unassemble(u8* start, u64 size) {
                     if (index != 0b100) {
                         print(" +");
                     }
-                    print(" [base(%s)]", SIB_base_registers[base]);
+                    print(" [base(%s)", SIB_base_registers[base]);
                 }
 
                 if (disp_bytes_count) {
-                    print(" + offset(0x%x)", disp);
+                    print(" + offset(0x%x)]", disp);
+                } else {
+                    print("]");
                 }
             }
         }
diff --git a/src/utils.c b/src/utils.c
index b0c95a9..1de19f9 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -127,7 +127,7 @@ void i64toa(i64 number, char* str, u32 base) {
     };
     u32 remainder = 0U;
     u32 size = 0U;
-    u64 u_number = ~number + 1;
+    u64 u_number = (number < 0) ? (~number + 1) : (number);
 
     if (number == 0) {
         str[0U] = codes[0U];
-- 
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