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| tpt_status | tpt_dct3_f32 (f32_t *aOutData, f32_t *aInData, f32_t *aScratch, size_t aLogN, bool aIdctFlag) |
| | Processing function for the floating-point DCT3. More...
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| tpt_status | tpt_dct3_f64 (f64_t *aOutData, f64_t *aInData, f64_t *aScratch, size_t aLogN, bool aIdctFlag) |
| | Processing function for the floating-point DCT3. More...
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| tpt_status | tpt_dct3_q15 (q15_t *aOutData, q15_t *aInData, q15_t *aScratch, size_t aLogN, bool aIdctFlag) |
| | Processing function for the Q15 DCT3. More...
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| tpt_status | tpt_dct3_q31 (q31_t *aOutData, q31_t *aInData, q31_t *aScratch, size_t aLogN, bool aIdctFlag) |
| | Processing function for the Q31 DCT3. More...
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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 III (IDCT type II) Function:
N-1
x[k] = sum { c[n] * y[n] * cos(PI * (2 * k + 1) * n / (2 * N)) }
n=0
where c[0] = 1 / 2.0 and c[n] = 1 for n != 0. The N-point DCT3 internally uses N-point CFFT implementation. It supports lengths of [16, 32, 64, ..., 1024] and the corresponding aLogN value is [4, 5, 6, ..., 10].
- Normalizing factor
- The normalizing factor is 1.0. If necessary, the caller should calculate the normalizing factor separately.
◆ tpt_dct3_f32()
Processing function for the floating-point DCT3.
- Parameters
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| [out] | aOutData | points to the output buffer. |
| [in] | aInData | points to the input buffer. |
| [in] | aScratch | points to a temporary buffer of size 2^(aLogN+1). |
| [in] | aLogN | The length is 2^aLogN. |
- Returns
- execution status
◆ tpt_dct3_f64()
Processing function for the floating-point DCT3.
- Parameters
-
| [in,out] | aInPlace | points to the in-place input and output buffer. |
| [in] | aScratch | points to a temporary buffer of size 2^(aLogN+1). |
| [in] | aLogN | The length is 2^aLogN. |
- Returns
- execution status
◆ tpt_dct3_q15()
Processing function for the Q15 DCT3.
- Parameters
-
| [out] | aOutData | points to the output buffer. |
| [in] | aInData | points to the input buffer. |
| [in] | aScratch | points to a temporary buffer of size 2^(aLogN+1). |
| [in] | aLogN | The length is 2^aLogN. |
- Returns
- execution status
- Input an output formats
- Internally inputs are downscaled in the CFFT 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:
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Input and Output Formats for Q15 DCT3
| aLogN | DCT3 Size | Input format | Output format | Number of bits to upscale |
| 4 | 16 | 1.15 | 5.11 | 4 |
| 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_dct3_q31()
Processing function for the Q31 DCT3.
- Parameters
-
| [out] | aOutData | points to the output buffer. |
| [in] | aInData | points to the input buffer. |
| [in] | aScratch | points to a temporary buffer of size 2^(aLogN+1). |
| [in] | aLogN | The length is 2^aLogN. |
- Returns
- execution status
- Input an output formats
- Internally inputs are downscaled in the CFFT 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:
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Input and Output Formats for Q31 DCT3
| aLogN | DCT3 Size | Input format | Output format | Number of bits to upscale |
| 4 | 16 | 1.31 | 5.27 | 0 |
| 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 |
| ...... |
1.9.1