DCT Type II Functions

Collaboration diagram for DCT Type II Functions:

Functions
tpt_status	tpt_dct2_f32 (f32_t *aOutData, f32_t *aInData, f32_t *aScratch, size_t aLogN, bool aIdctFlag)
	Processing function for the floating-point DCT2. More...
tpt_status	tpt_dct2_f64 (f64_t *aOutData, f64_t *aInData, f64_t *aScratch, size_t aLogN, bool aIdctFlag)
	Processing function for the floating-point DCT2. More...
tpt_status	tpt_dct2_q15 (q15_t *aOutData, q15_t *aInData, q15_t *aScratch, size_t aLogN, bool aIdctFlag)
	Processing function for the Q15 DCT2. More...
tpt_status	tpt_dct2_q31 (q31_t *aOutData, q31_t *aInData, q31_t *aScratch, size_t aLogN, bool aIdctFlag)
	Processing function for the Q31 DCT2. More...

Detailed Description

A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies. In particular, a DCT is a Fourier-related transform similar to the discrete Fourier transform (DFT), but using only real numbers.

Algorithm

This function implements DCT Type II Function:

           N-1
    y[k] = sum { x[n] * cos(PI * (2 * n + 1) * k / (2 * N)) }
           n=0
  

The N-point DCT2 internally uses N-point RFFT implementation. It supports lengths of [32, 64, 128, ..., 1024] and the corresponding aLogN value is [5, 6, 7, ..., 10].

Normalizing factor

The normalizing factor is 1.0. If necessary, the caller should calculate the normalizing factor separately.

Function Documentation

tpt_dct2_f32()

tpt_status tpt_dct2_f32	(	f32_t *	aOutData,
		f32_t *	aInData,
		f32_t *	aScratch,
		size_t	aLogN,
		bool	aIdctFlag
	)

Processing function for the floating-point DCT2.

Source buffer is modified by this function.

Parameters

[out]	aOutData	points to output buffer.
[in]	aInData	points to input buffer (Source buffer is modified by this function.)
[in]	aScratch	points to a temporary buffer of size 2^(aLogN+1).
[in]	aLogN	The length is 2^aLogN.

Returns

execution status

• TPT_MATH_SUCCESS : Operation is successful.
• TPT_MATH_ARGUMENT_ERROR : aLogN is not supported.

tpt_dct2_f64()

tpt_status tpt_dct2_f64	(	f64_t *	aOutData,
		f64_t *	aInData,
		f64_t *	aScratch,
		size_t	aLogN,
		bool	aIdctFlag
	)

Processing function for the floating-point DCT2.

Source buffer is modified by this function.

Parameters

[out]	aOutData	points to output buffer.
[in]	aInData	points to input buffer (Source buffer is modified by this function.)
[in]	aScratch	points to a temporary buffer of size 2^(aLogN+1).
[in]	aLogN	The length is 2^aLogN.

Returns

execution status

• TPT_MATH_SUCCESS : Operation is successful.
• TPT_MATH_ARGUMENT_ERROR : aLogN is not supported.

tpt_dct2_q15()

tpt_status tpt_dct2_q15	(	q15_t *	aOutData,
		q15_t *	aInData,
		q15_t *	aScratch,
		size_t	aLogN,
		bool	aIdctFlag
	)

Processing function for the Q15 DCT2.

Source buffer is modified by this function.

Parameters

[out]	aOutData	points to output buffer.
[in]	aInData	points to input buffer (Source buffer is modified by this function.)
[in]	aScratch	points to a temporary buffer of size 2^(aLogN+1).
[in]	aLogN	The length is 2^aLogN.

Returns

execution status

• TPT_MATH_SUCCESS : Operation is successful.
• TPT_MATH_ARGUMENT_ERROR : aLogN is not supported.

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:

Input and Output Formats for Q15 DCT2

aLogN	DCT2 Size	Input format	Output format	Number of bits to upscale
5	32	1.15	6.10	5
6	64	1.15	7.9	6
7	128	1.15	8.8	7
8	256	1.15	9.7	8
9	512	1.15	10.6	9
10	1024	1.15	11.5	10
......

tpt_dct2_q31()

tpt_status tpt_dct2_q31	(	q31_t *	aOutData,
		q31_t *	aInData,
		q31_t *	aScratch,
		size_t	aLogN,
		bool	aIdctFlag
	)

Processing function for the Q31 DCT2.

Source buffer is modified by this function.

Parameters

[out]	aOutData	points to output buffer.
[in]	aInData	points to input buffer (Source buffer is modified by this function.)
[in]	aScratch	points to a temporary buffer of size 2^(aLogN+1).
[in]	aLogN	The length is 2^aLogN.

Returns

execution status

• TPT_MATH_SUCCESS : Operation is successful.
• TPT_MATH_ARGUMENT_ERROR : aLogN is not supported.

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:

Input and Output Formats for Q31 DCT2

aLogN	DCT2 Size	Input format	Output format	Number of bits to upscale
5	32	1.31	6.26	5
6	64	1.31	7.25	6
7	128	1.31	8.24	7
8	256	1.31	9.23	8
9	512	1.31	10.22	9
10	1024	1.31	11.21	10
......