-// Floating-point IDCT due to Arai, Agui and Nakajima (also known as AA&N).
-// See idct.c for more details.
-void idct_float(const int16_t* input, const uint32_t* quant_table, uint8_t* output);
+// void idct_example(const int16_t* input, const void* userdata, uint8_t* output);
+// userdata is the same as returned by the alloc function.
+typedef void (idct_func_t)(const int16_t*, const void*, uint8_t*);