+void* idct_reference_alloc(const uint32_t* quant_table);
+void idct_reference_free(void* userdata);
+void idct_reference(const int16_t* input, const void* userdata, uint8_t* output);
+
+// Floating-point IDCT due to Arai, Agui and Nakajima (also known as AA&N).
+// See idct.c for more details.
+void* idct_float_alloc(const uint32_t* quant_table);
+void idct_float_free(void* userdata);
+void idct_float(const int16_t* input, const void* userdata, uint8_t* output);