Added SDL_StepBackUTF8()

src/dynapi/SDL_dynapi.sym

@@ -1176,6 +1176,7 @@ SDL3_0.0.0 {
     SDL_wcsnstr;
     SDL_wcsstr;
     SDL_wcstol;
+    SDL_StepBackUTF8;
     # extra symbols go here (don't modify this line)
   local: *;
 };

src/dynapi/SDL_dynapi_overrides.h

@@ -1201,3 +1201,4 @@
 #define SDL_wcsnstr SDL_wcsnstr_REAL
 #define SDL_wcsstr SDL_wcsstr_REAL
 #define SDL_wcstol SDL_wcstol_REAL
+#define SDL_StepBackUTF8 SDL_StepBackUTF8_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -1207,3 +1207,4 @@ SDL_DYNAPI_PROC(size_t,SDL_wcsnlen,(const wchar_t *a, size_t b),(a,b),return)
 SDL_DYNAPI_PROC(wchar_t*,SDL_wcsnstr,(const wchar_t *a, const wchar_t *b, size_t c),(a,b,c),return)
 SDL_DYNAPI_PROC(wchar_t*,SDL_wcsstr,(const wchar_t *a, const wchar_t *b),(a,b),return)
 SDL_DYNAPI_PROC(long,SDL_wcstol,(const wchar_t *a, wchar_t **b, int c),(a,b,c),return)
+SDL_DYNAPI_PROC(Uint32,SDL_StepBackUTF8,(const char *a, const char **b),(a,b),return)

src/stdlib/SDL_string.c

@@ -265,6 +265,26 @@ Uint32 SDL_StepUTF8(const char **pstr, size_t *pslen)
     return result;
 }
 
+Uint32 SDL_StepBackUTF8(const char *start, const char **pstr)
+{
+    if (!pstr || *pstr <= start) {
+        return 0;
+    }
+
+    // Step back over the previous UTF-8 character
+    const char *str = *pstr;
+    do {
+        if (str == start) {
+            break;
+        }
+        --str;
+    } while ((*str & 0xC0) == 0x80);
+
+    size_t length = (*pstr - str);
+    *pstr = str;
+    return StepUTF8(&str, length);
+}
+
 #if (SDL_SIZEOF_WCHAR_T == 2)
 static Uint32 StepUTF16(const Uint16 **_str, const size_t slen)
 {