CMSIS-DSP  
CMSIS DSP Software Library
 
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Functions

arm_status arm_dct4_init_q15 (arm_dct4_instance_q15 *S, arm_rfft_instance_q15 *S_RFFT, arm_cfft_radix4_instance_q15 *S_CFFT, uint16_t N, uint16_t Nby2, q15_t normalize)
 Initialization function for the Q15 DCT4/IDCT4.
 
void arm_dct4_q15 (const arm_dct4_instance_q15 *S, q15_t *pState, q15_t *pInlineBuffer)
 Processing function for the Q15 DCT4/IDCT4.
 

Description

Function Documentation

◆ arm_dct4_init_q15()

arm_status arm_dct4_init_q15 ( arm_dct4_instance_q15 S,
arm_rfft_instance_q15 S_RFFT,
arm_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]Spoints to an instance of Q15 DCT4/IDCT4 structure
[in]S_RFFTpoints to an instance of Q15 RFFT/RIFFT structure
[in]S_CFFTpoints to an instance of Q15 CFFT/CIFFT structure
[in]Nlength of the DCT4
[in]Nby2half of the length of the DCT4
[in]normalizenormalizing factor
Returns
execution status
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

◆ arm_dct4_q15()

void arm_dct4_q15 ( const arm_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]Spoints to an instance of the Q15 DCT4 structure.
[in]pStatepoints to state buffer.
[in,out]pInlineBufferpoints 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