Added SDL_crc16() to be used in joystick GUIDs after 2.24.0

WhatsNew.txt

@@ -18,7 +18,7 @@ General:
       * The patchlevel indicates successive prereleases, for example
         2.23.1 and 2.23.2 would be prereleases during development of
         the SDL 2.24.0 stable release.
-* Added SDL_bsearch() and SDL_utf8strnlen() to the stdlib routines
+* Added SDL_bsearch(), SDL_crc16(), and  SDL_utf8strnlen() to the stdlib routines
 * Added SDL_size_mul_overflow() and SDL_size_add_overflow() for better size overflow protection
 * Added SDL_ResetHint() to reset a hint to the default value
 * The hint SDL_HINT_JOYSTICK_HIDAPI_JOY_CONS now defaults on

include/SDL_stdinc.h

@@ -503,6 +503,7 @@ extern DECLSPEC int SDLCALL SDL_isgraph(int x);
 extern DECLSPEC int SDLCALL SDL_toupper(int x);
 extern DECLSPEC int SDLCALL SDL_tolower(int x);
 
+extern DECLSPEC Uint16 SDLCALL SDL_crc16(Uint16 crc, const void *data, size_t len);
 extern DECLSPEC Uint32 SDLCALL SDL_crc32(Uint32 crc, const void *data, size_t len);
 
 extern DECLSPEC void *SDLCALL SDL_memset(SDL_OUT_BYTECAP(len) void *dst, int c, size_t len);

src/dynapi/SDL2.exports

@@ -857,3 +857,4 @@
 ++'_SDL_GetPointDisplayIndex'.'SDL2.dll'.'SDL_GetPointDisplayIndex'
 ++'_SDL_GetRectDisplayIndex'.'SDL2.dll'.'SDL_GetRectDisplayIndex'
 ++'_SDL_ResetHint'.'SDL2.dll'.'SDL_ResetHint'
+++'_SDL_crc16'.'SDL2.dll'.'SDL_crc16'

src/dynapi/SDL_dynapi_overrides.h

@@ -883,3 +883,4 @@
 #define SDL_GetPointDisplayIndex SDL_GetPointDisplayIndex_REAL
 #define SDL_GetRectDisplayIndex SDL_GetRectDisplayIndex_REAL
 #define SDL_ResetHint SDL_ResetHint_REAL
+#define SDL_crc16 SDL_crc16_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -966,3 +966,4 @@ SDL_DYNAPI_PROC(int,SDL_GetDefaultAudioInfo,(char **a, SDL_AudioSpec *b, int c),
 SDL_DYNAPI_PROC(int,SDL_GetPointDisplayIndex,(const SDL_Point *a),(a),return)
 SDL_DYNAPI_PROC(int,SDL_GetRectDisplayIndex,(const SDL_Rect *a),(a),return)
 SDL_DYNAPI_PROC(SDL_bool,SDL_ResetHint,(const char *a),(a),return)
+SDL_DYNAPI_PROC(Uint16,SDL_crc16,(Uint16 a, const void *b, size_t c),(a,b,c),return)

src/stdlib/SDL_crc16.c

@@ -0,0 +1,54 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2022 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "../SDL_internal.h"
+
+#include "SDL_stdinc.h"
+
+
+/* Public domain CRC implementation adapted from:
+   http://home.thep.lu.se/~bjorn/crc/crc32_simple.c
+*/
+/* NOTE: DO NOT CHANGE THIS ALGORITHM
+   There is code that relies on this in the joystick code
+*/
+
+static Uint16 crc16_for_byte(Uint8 r)
+{
+    Uint16 crc = 0;
+    int i;
+    for (i = 0; i < 8; ++i) {
+        crc = ((crc ^ r) & 1? 0xA001 : 0) ^ crc >> 1;
+        r >>= 1;
+    }
+    return crc;
+}
+
+Uint16 SDL_crc16(Uint16 crc, const void *data, size_t len)
+{
+    /* As an optimization we can precalculate a 256 entry table for each byte */
+    size_t i;
+    for(i = 0; i < len; ++i) {
+        crc = crc16_for_byte((Uint8)crc ^ ((const Uint8*)data)[i]) ^ crc >> 8;
+    }
+    return crc;
+}
+
+/* vi: set ts=4 sw=4 expandtab: */