From e3133b775ebda7599bd1f45a903db3a75b6d8496 Mon Sep 17 00:00:00 2001
From: Jamie Reece Wilson <me@reece.sx>
Date: Sat, 21 Sep 2024 22:02:41 +0100
Subject: [PATCH] [+] AuBitReverse (+ aliases: AuReverseBits, AuBitsReverse)

---
 Include/auROXTL/auBitsUtils.hpp | 125 ++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/Include/auROXTL/auBitsUtils.hpp b/Include/auROXTL/auBitsUtils.hpp
index 06eac47..a53bd87 100644
--- a/Include/auROXTL/auBitsUtils.hpp
+++ b/Include/auROXTL/auBitsUtils.hpp
@@ -7,6 +7,53 @@
 ***/
 #pragma once
 
+// options: _AU_FORCE_NO_FLIP8_MAP, _AU_DO_NOT_USE_BITFLIP_U16, _AU_DO_NOT_USE_BITFLIP_U32
+namespace __audetail
+{
+    inline const constexpr AuUInt8 kFlipBitsU4Lookup[16] {
+        0x0, 0x8, 0x4, 0xc, 0x2, 0xa, 0x6, 0xe,
+        0x1, 0x9, 0x5, 0xd, 0x3, 0xb, 0x7, 0xf
+    };
+
+#if !defined(_AU_FORCE_NO_FLIP8_MAP)
+#define _AU_HAS_FLIP8
+    inline const constexpr AuUInt8 kFlipBitsU8Lookup[256] {
+        0, 128, 64, 192, 32, 160, 96, 224,
+        16, 144, 80, 208, 48, 176, 112, 240,
+        8, 136, 72, 200, 40, 168, 104, 232,
+        24, 152, 88, 216, 56, 184, 120, 248,
+        4, 132, 68, 196, 36, 164, 100, 228,
+        20, 148, 84, 212, 52, 180, 116, 244,
+        12, 140, 76, 204, 44, 172, 108, 236,
+        28, 156, 92, 220, 60, 188, 124, 252,
+        2, 130, 66, 194, 34, 162, 98, 226,
+        18, 146, 82, 210, 50, 178, 114, 242,
+        10, 138, 74, 202, 42, 170, 106, 234,
+        26, 154, 90, 218, 58, 186, 122, 250,
+        6, 134, 70, 198, 38, 166, 102, 230,
+        22, 150, 86, 214, 54, 182, 118, 246,
+        14, 142, 78, 206, 46, 174, 110, 238,
+        30, 158, 94, 222, 62, 190, 126, 254,
+        1, 129, 65, 193, 33, 161, 97, 225,
+        17, 145, 81, 209, 49, 177, 113, 241,
+        9, 137, 73, 201, 41, 169, 105, 233,
+        25, 153, 89, 217, 57, 185, 121, 249,
+        5, 133, 69, 197, 37, 165, 101, 229,
+        21, 149, 85, 213, 53, 181, 117, 245,
+        13, 141, 77, 205, 45, 173, 109, 237,
+        29, 157, 93, 221, 61, 189, 125, 253,
+        3, 131, 67, 195, 35, 163, 99, 227,
+        19, 147, 83, 211, 51, 179, 115, 243,
+        11, 139, 75, 203, 43, 171, 107, 235,
+        27, 155, 91, 219, 59, 187, 123, 251,
+        7, 135, 71, 199, 39, 167, 103, 231,
+        23, 151, 87, 215, 55, 183, 119, 247,
+        15, 143, 79, 207, 47, 175, 111, 239,
+        31, 159, 95, 223, 63, 191, 127, 255
+    };
+#endif
+}
+
 template <class T>
 static auline bool AuTestBit(T value, AuUInt8 idx)
 {
@@ -325,4 +372,82 @@ static AuUInt8 AuPopCnt(T in)
     }
     
     return {};
+}
+
+template<typename T>
+constexpr T AuBitReverse(T uBits);
+
+template <>
+constexpr AuUInt8 AuBitReverse(AuUInt8 uBits)
+{
+    return (__audetail::kFlipBitsU8Lookup[uBits & 0b1111] << 4) |
+           (__audetail::kFlipBitsU8Lookup[uBits >> 4]           );
+
+}
+
+template <>
+constexpr AuUInt16 AuBitReverse(AuUInt16 uBits)
+{
+#if !defined(_AU_DO_NOT_USE_BITFLIP_U16)
+    uBits = ((uBits >> 1) & 0x5555u) | ((uBits & 0x5555u) << 1);
+    uBits = ((uBits >> 2) & 0x3333u) | ((uBits & 0x3333u) << 2);
+    uBits = ((uBits >> 4) & 0x0f0fu) | ((uBits & 0x0f0fu) << 4);
+    uBits = ((uBits >> 8) & 0x00ffu) | ((uBits & 0x00ffu) << 8);
+    return uBits;
+#endif
+
+#if !defined(_AU_HAS_FLIP8)
+    return AuUInt16(AuBitReverse(AuUInt8((uBits >> 8u) & 0xFFu)))       |
+           AuUInt16(AuUInt16(AuBitReverse(AuUInt8(uBits & 0xFFu))) << 8u);
+#else
+    return 0 |
+        AuUInt32(__audetail::kFlipBitsU8Lookup[(uBits >> 8) & 0xFF]) << 0u |
+        AuUInt32(__audetail::kFlipBitsU8Lookup[(uBits >> 0) & 0xFF]) << 8u;
+#endif
+}
+
+template <>
+constexpr AuUInt32 AuBitReverse(AuUInt32 uBits)
+{
+#if !defined(_AU_DO_NOT_USE_BITFLIP_U32)
+    uBits = ((uBits >> 1) & 0x55555555u) | ((uBits & 0x55555555u) << 1);
+    uBits = ((uBits >> 2) & 0x33333333u) | ((uBits & 0x33333333u) << 2);
+    uBits = ((uBits >> 4) & 0x0f0f0f0fu) | ((uBits & 0x0f0f0f0fu) << 4);
+    uBits = ((uBits >> 8) & 0x00ff00ffu) | ((uBits & 0x00ff00ffu) << 8);
+    uBits = ((uBits >> 16) & 0xffffu) | ((uBits & 0xffffu) << 16);
+    return uBits;
+#endif
+
+#if !defined(_AU_HAS_FLIP8)
+    return 0 |
+           AuUInt32(AuBitReverse<AuUInt8>((uBits >> 24) & 0xFF)) << 0ul |
+           AuUInt32(AuBitReverse<AuUInt8>((uBits >> 16) & 0xFF)) << 8ul |
+           AuUInt32(AuBitReverse<AuUInt8>((uBits >> 8) & 0xFF)) << 16ul |
+           AuUInt32(AuBitReverse<AuUInt8>((uBits >> 0) & 0xFF)) << 24ul;
+#else
+    return 0 |
+           AuUInt32(__audetail::kFlipBitsU8Lookup[(uBits >> 24) & 0xFF]) << 0ul |
+           AuUInt32(__audetail::kFlipBitsU8Lookup[(uBits >> 16) & 0xFF]) << 8ul |
+           AuUInt32(__audetail::kFlipBitsU8Lookup[(uBits >> 8) & 0xFF]) << 16ul |
+           AuUInt32(__audetail::kFlipBitsU8Lookup[(uBits >> 0) & 0xFF]) << 24ul;
+#endif
+}
+
+template <>
+constexpr AuUInt64 AuBitReverse(AuUInt64 uBits)
+{
+    return AuUInt64(AuBitReverse(AuUInt32((uBits >> 32ull) & 0xFFFFFFFFul)))      |
+           AuUInt64(AuUInt64(AuBitReverse(AuUInt32(uBits & 0xFFFFFFFFul))) << 32UL);
+}
+
+template<typename T>
+constexpr T AuBitsReverse(T uBits)
+{
+    return AuBitReverse<T>(uBits);
+}
+
+template<typename T>
+constexpr T AuReverseBits(T uBits)
+{
+    return AuBitReverse<T>(uBits);
 }
\ No newline at end of file