DCT4 Q15

Functions
RISCV_DSP_ATTRIBUTE riscv_status	riscv_dct4_init_q15 (riscv_dct4_instance_q15 *S, riscv_rfft_instance_q15 *S_RFFT, riscv_cfft_radix4_instance_q15 *S_CFFT, uint16_t N, uint16_t Nby2, q15_t normalize)
	Initialization function for the Q15 DCT4/IDCT4. More...
RISCV_DSP_ATTRIBUTE void	riscv_dct4_q15 (const riscv_dct4_instance_q15 *S, q15_t *pState, q15_t *pInlineBuffer)
	Processing function for the Q15 DCT4/IDCT4. More...

Detailed Description

Function Documentation

riscv_dct4_init_q15()

RISCV_DSP_ATTRIBUTE riscv_status riscv_dct4_init_q15	(	riscv_dct4_instance_q15 *	S,
		riscv_rfft_instance_q15 *	S_RFFT,
		riscv_cfft_radix4_instance_q15 *	S_CFFT,
		uint16_t	N,
		uint16_t	Nby2,
		q15_t	normalize
	)

Initialization function for the Q15 DCT4/IDCT4.

Deprecated:

Do not use this function. It will be removed in future versions.

Parameters

[in,out]	S	points to an instance of Q15 DCT4/IDCT4 structure
[in]	S_RFFT	points to an instance of Q15 RFFT/RIFFT structure
[in]	S_CFFT	points to an instance of Q15 CFFT/CIFFT structure
[in]	N	length of the DCT4
[in]	Nby2	half of the length of the DCT4
[in]	normalize	normalizing factor

Returns

execution status

• RISCV_MATH_SUCCESS : Operation successful
• RISCV_MATH_ARGUMENT_ERROR : N is not a supported transform length

Normalizing factor

The normalizing factor is sqrt(2/N), which depends on the size of transform N. Normalizing factors in 1.15 format are mentioned in the table below for different DCT sizes:

DCT Size	Normalizing factor value (hexadecimal)
2048	0x400
512	0x800
128	0x1000

riscv_dct4_q15()

RISCV_DSP_ATTRIBUTE void riscv_dct4_q15	(	const riscv_dct4_instance_q15 *	S,
		q15_t *	pState,
		q15_t *	pInlineBuffer
	)

Processing function for the Q15 DCT4/IDCT4.

Deprecated:

Do not use this function. It will be removed in future versions.

Parameters

[in]	S	points to an instance of the Q15 DCT4 structure.
[in]	pState	points to state buffer.
[in,out]	pInlineBuffer	points to the in-place input and output buffer.

Input an output formats

Internally inputs are downscaled in the RFFT process function to avoid overflows. Number of bits downscaled, depends on the size of the transform. The input and output formats for different DCT sizes and number of bits to upscale are mentioned in the table below:

DCT Size	Input format	Output format	Number of bits to upscale
2048	1.15	11.5	10
512	1.15	9.7	8
128	1.15	7.9	6