From e34b0160f185b61a5f5411a9b198421a0387efae Mon Sep 17 00:00:00 2001
From: Dekkonot <git@dekkonot.com>
Date: Mon, 16 Oct 2023 17:34:40 -0700
Subject: [PATCH] Add normal implementation of bit32.byteswap

---
 Analysis/src/EmbeddedBuiltinDefinitions.cpp |  1 +
 VM/src/lbitlib.cpp                          | 13 +++++++++++++
 docs/_pages/library.md                      |  6 ++++++
 3 files changed, 20 insertions(+)

diff --git a/Analysis/src/EmbeddedBuiltinDefinitions.cpp b/Analysis/src/EmbeddedBuiltinDefinitions.cpp
index 65b04d62..dd2a5d19 100644
--- a/Analysis/src/EmbeddedBuiltinDefinitions.cpp
+++ b/Analysis/src/EmbeddedBuiltinDefinitions.cpp
@@ -21,6 +21,7 @@ declare bit32: {
     replace: (n: number, v: number, field: number, width: number?) -> number,
     countlz: (n: number) -> number,
     countrz: (n: number) -> number,
+    byteswap: (n: number) -> number,
 }
 
 declare math: {
diff --git a/VM/src/lbitlib.cpp b/VM/src/lbitlib.cpp
index 47445b80..65572501 100644
--- a/VM/src/lbitlib.cpp
+++ b/VM/src/lbitlib.cpp
@@ -5,6 +5,8 @@
 #include "lcommon.h"
 #include "lnumutils.h"
 
+LUAU_FASTFLAG(LuauBit32Byteswap)
+
 #define ALLONES ~0u
 #define NBITS int(8 * sizeof(unsigned))
 
@@ -210,6 +212,16 @@ static int b_countrz(lua_State* L)
     return 1;
 }
 
+static int b_swap(lua_State* L)
+{
+    LUAU_ASSERT(FFlag::LuauBit32Byteswap);
+    b_uint n = luaL_checkunsigned(L, 1);
+    n = ((n >> 24) & 0xff) | ((n << 8) & 0xff0000) | ((n >> 8) & 0xff00) | ((n << 24) & 0xff000000);
+
+    lua_pushunsigned(L, n);
+    return 1;
+}
+
 static const luaL_Reg bitlib[] = {
     {"arshift", b_arshift},
     {"band", b_and},
@@ -225,6 +237,7 @@ static const luaL_Reg bitlib[] = {
     {"rshift", b_rshift},
     {"countlz", b_countlz},
     {"countrz", b_countrz},
+    {"byteswap", b_swap},
     {NULL, NULL},
 };
 
diff --git a/docs/_pages/library.md b/docs/_pages/library.md
index d6d1bc7f..8633b332 100644
--- a/docs/_pages/library.md
+++ b/docs/_pages/library.md
@@ -728,6 +728,12 @@ function bit32.countrz(n: number): number
 
 Returns the number of consecutive zero bits in the 32-bit representation of `n` starting from the right-most (least significant) bit. Returns 32 if `n` is zero.
 
+```
+function bit32.byteswap(n: number): number
+```
+
+Returns `n` with the order of the bytes swappped.
+
 ## utf8 library
 
 Strings in Luau can contain arbitrary bytes; however, in many applications strings representing text contain UTF8 encoded data by convention, that can be inspected and manipulated using `utf8` library.