FFstrbuf: add function ffStrbufSubstr

src/util/FFstrbuf.c

@@ -398,7 +398,8 @@ bool ffStrbufSubstrBefore(FFstrbuf* strbuf, uint32_t index)
     if(strbuf->allocated == 0)
     {
         //static string
-        ffStrbufInitNS(strbuf, strbuf->length, strbuf->chars);
+        if (index < strbuf->length)
+            ffStrbufInitNS(strbuf, index, strbuf->chars);
         return true;
     }
 
@@ -461,6 +462,26 @@ bool ffStrbufSubstrAfterLastC(FFstrbuf* strbuf, char c)
     return true;
 }
 
+bool ffStrbufSubstr(FFstrbuf* strbuf, uint32_t start, uint32_t end)
+{
+    if (__builtin_expect(start >= end, false))
+    {
+        ffStrbufClear(strbuf);
+        return false;
+    }
+
+    if (__builtin_expect(start == 0, false)) return ffStrbufSubstrBefore(strbuf, end);
+    if (__builtin_expect(end >= strbuf->length, false)) return ffStrbufSubstrAfter(strbuf, start - 1);
+
+    uint32_t len = end - start;
+    ffStrbufEnsureFixedLengthFree(strbuf, len); // In case of static string
+    memmove(strbuf->chars, strbuf->chars + start, len);
+
+    strbuf->length = len;
+    strbuf->chars[len] = '\0';
+    return true;
+}
+
 uint32_t ffStrbufCountC(const FFstrbuf* strbuf, char c)
 {
     uint32_t result = 0;

src/util/FFstrbuf.h

@@ -73,6 +73,7 @@ bool ffStrbufSubstrAfter(FFstrbuf* strbuf, uint32_t index); // Not including the
 bool ffStrbufSubstrAfterFirstC(FFstrbuf* strbuf, char c);
 bool ffStrbufSubstrAfterFirstS(FFstrbuf* strbuf, const char* str);
 bool ffStrbufSubstrAfterLastC(FFstrbuf* strbuf, char c);
+bool ffStrbufSubstr(FFstrbuf* strbuf, uint32_t start, uint32_t end);
 
 FF_C_NODISCARD uint32_t ffStrbufCountC(const FFstrbuf* strbuf, char c);
 

tests/strbuf.c

@@ -665,6 +665,52 @@ int main(void)
         VERIFY(ffStrbufMatchSeparatedS(&strbuf, ":abc", ':') == true);
     }
 
+    {
+        ffStrbufSetStatic(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 0, 1); // start, end
+        VERIFY(ffStrbufEqualS(&strbuf, "a"));
+
+        ffStrbufSetStatic(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 1, 1);
+        VERIFY(ffStrbufEqualS(&strbuf, ""));
+
+        ffStrbufSetStatic(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 2, 1);
+        VERIFY(ffStrbufEqualS(&strbuf, ""));
+
+        ffStrbufSetStatic(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 2, 3);
+        VERIFY(ffStrbufEqualS(&strbuf, "c"));
+
+        ffStrbufSetStatic(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 0, 3);
+        VERIFY(ffStrbufEqualS(&strbuf, "abc"));
+    }
+
+    {
+        ffStrbufSetS(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 0, 1); // start, end
+        VERIFY(ffStrbufEqualS(&strbuf, "a"));
+
+        ffStrbufSetS(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 1, 1);
+        VERIFY(ffStrbufEqualS(&strbuf, ""));
+
+        ffStrbufSetS(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 2, 1);
+        VERIFY(ffStrbufEqualS(&strbuf, ""));
+
+        ffStrbufSetS(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 2, 3);
+        VERIFY(ffStrbufEqualS(&strbuf, "c"));
+
+        ffStrbufSetS(&strbuf, "abc");
+        ffStrbufSubstr(&strbuf, 0, 3);
+        VERIFY(ffStrbufEqualS(&strbuf, "abc"));
+
+        ffStrbufDestroy(&strbuf);
+    }
+
     //Success
     puts("\e[32mAll tests passed!" FASTFETCH_TEXT_MODIFIER_RESET);
 }