From 326dc95f9c7ab7adf6ee63f4221b64b4002b6bed Mon Sep 17 00:00:00 2001
From: Teselka <53512153+Teselka@users.noreply.github.com>
Date: Wed, 20 Nov 2024 13:10:36 +0200
Subject: [PATCH] Misc: use native crc32 instructions on SEE 4.2 targets.
 (#8169, #4933)

---
 docs/CHANGELOG.txt |  1 +
 imgui.cpp          | 18 ++++++++++++++++++
 imgui_internal.h   |  4 ++++
 3 files changed, 23 insertions(+)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index e901e437e..b93888c85 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -62,6 +62,7 @@ Other changes:
 - Tools: binary_to_compressed_c: added -u8/-u32/-base85 export options.
 - Demo: example tree used by Property Editor & Selection demos properly freed
   on application closure. (#8158) [@Legulysse]
+- Misc: use SSE 4.2 crc32 instructions when available. (#8169, #4933) [@Teselka]
 - Backends: Vulkan: Make user-provided descriptor pool optional. As a convenience,
   when setting init_info->DescriptorPoolSize then the backend will create and manage
   one itself. (#8172, #4867) [@zeux]
diff --git a/imgui.cpp b/imgui.cpp
index 072c09799..ff5d25408 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -2150,6 +2150,7 @@ void ImFormatStringToTempBufferV(const char** out_buf, const char** out_buf_end,
     }
 }
 
+#ifndef IMGUI_ENABLE_SSE4_2
 // CRC32 needs a 1KB lookup table (not cache friendly)
 // Although the code to generate the table is simple and shorter than the table itself, using a const table allows us to easily:
 // - avoid an unnecessary branch/memory tap, - keep the ImHashXXX functions usable by static constructors, - make it thread-safe.
@@ -2173,6 +2174,7 @@ static const ImU32 GCrc32LookupTable[256] =
     0xE330A81A,0x115B2B19,0x020BD8ED,0xF0605BEE,0x24AA3F05,0xD6C1BC06,0xC5914FF2,0x37FACCF1,0x69E9F0D5,0x9B8273D6,0x88D28022,0x7AB90321,0xAE7367CA,0x5C18E4C9,0x4F48173D,0xBD23943E,
     0xF36E6F75,0x0105EC76,0x12551F82,0xE03E9C81,0x34F4F86A,0xC69F7B69,0xD5CF889D,0x27A40B9E,0x79B737BA,0x8BDCB4B9,0x988C474D,0x6AE7C44E,0xBE2DA0A5,0x4C4623A6,0x5F16D052,0xAD7D5351
 };
+#endif
 
 // Known size hash
 // It is ok to call ImHashData on a string with known length but the ### operator won't be supported.
@@ -2181,10 +2183,16 @@ ImGuiID ImHashData(const void* data_p, size_t data_size, ImGuiID seed)
 {
     ImU32 crc = ~seed;
     const unsigned char* data = (const unsigned char*)data_p;
+#ifndef IMGUI_ENABLE_SSE4_2
     const ImU32* crc32_lut = GCrc32LookupTable;
     while (data_size-- != 0)
         crc = (crc >> 8) ^ crc32_lut[(crc & 0xFF) ^ *data++];
     return ~crc;
+#else
+    while (data_size-- != 0)
+        crc = _mm_crc32_u8(crc, *data++);
+    return ~crc;
+#endif
 }
 
 // Zero-terminated string hash, with support for ### to reset back to seed value
@@ -2198,7 +2206,9 @@ ImGuiID ImHashStr(const char* data_p, size_t data_size, ImGuiID seed)
     seed = ~seed;
     ImU32 crc = seed;
     const unsigned char* data = (const unsigned char*)data_p;
+#ifndef IMGUI_ENABLE_SSE4_2
     const ImU32* crc32_lut = GCrc32LookupTable;
+#endif
     if (data_size != 0)
     {
         while (data_size-- != 0)
@@ -2206,7 +2216,11 @@ ImGuiID ImHashStr(const char* data_p, size_t data_size, ImGuiID seed)
             unsigned char c = *data++;
             if (c == '#' && data_size >= 2 && data[0] == '#' && data[1] == '#')
                 crc = seed;
+#ifndef IMGUI_ENABLE_SSE4_2
             crc = (crc >> 8) ^ crc32_lut[(crc & 0xFF) ^ c];
+#else
+            crc = _mm_crc32_u8(crc, c);
+#endif
         }
     }
     else
@@ -2215,7 +2229,11 @@ ImGuiID ImHashStr(const char* data_p, size_t data_size, ImGuiID seed)
         {
             if (c == '#' && data[0] == '#' && data[1] == '#')
                 crc = seed;
+#ifndef IMGUI_ENABLE_SSE4_2
             crc = (crc >> 8) ^ crc32_lut[(crc & 0xFF) ^ c];
+#else
+            crc = _mm_crc32_u8(crc, c);
+#endif
         }
     }
     return ~crc;
diff --git a/imgui_internal.h b/imgui_internal.h
index 40cf3c0c3..fd8a185a5 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -61,6 +61,10 @@ Index of this file:
 #if (defined __SSE__ || defined __x86_64__ || defined _M_X64 || (defined(_M_IX86_FP) && (_M_IX86_FP >= 1))) && !defined(IMGUI_DISABLE_SSE)
 #define IMGUI_ENABLE_SSE
 #include <immintrin.h>
+#if (defined __AVX__ || defined __SSE4_2__)
+#define IMGUI_ENABLE_SSE4_2
+#include <nmmintrin.h>
+#endif
 #endif
 
 // Visual Studio warnings