Punny __rt_ffs() does not use extra space

Author: pegasusplus

src/kservice.c

@@ -1026,7 +1026,37 @@ RTM_EXPORT(rt_free_align);
 #endif /* RT_USING_HEAP */
 
 #ifndef RT_USING_CPU_FFS
-#ifdef RT_USING_TINY_FFS
+#ifdef RT_USING_PUNY_FFS
+int __rt_ffs(rt_int32_t value) {
+    if (value == 0)
+        return 0; // 0 means no bit 1
+
+    int position = 1; // position start from 1
+
+    // search half range
+    if ((value & 0xFFFF) == 0) { // is lower 16bit 0
+        position += 16;
+        value >>= 16;
+    }
+    if ((value & 0xFF) == 0) { // is lower 8bit 0
+        position += 8;
+        value >>= 8;
+    }
+    if ((value & 0xF) == 0) { // is lower 4bit 0
+        position += 4;
+        value >>= 4;
+    }
+    if ((value & 0x3) == 0) { // is lower 2bit 0
+        position += 2;
+        value >>= 2;
+    }
+    if ((value & 0x1) == 0) { // is lower 1bit 0
+        position += 1;
+    }
+
+    return position;
+}
+#elif defined(RT_USING_TINY_FFS)
 const rt_uint8_t __lowest_bit_bitmap[] =
 {
     /*  0 - 7  */  0,  1,  2, 27,  3, 24, 28, 32,