RealFFT

Functions
void	arm_rfft_f32 (const arm_rfft_instance_f32 *S, float32_t *pSrc, float32_t *pDst)
	Processing function for the floating-point RFFT/RIFFT.
void	arm_rfft_fast_f32 (arm_rfft_fast_instance_f32 *S, float32_t *p, float32_t *pOut, uint8_t ifftFlag)
	Processing function for the floating-point real FFT.
arm_status	arm_rfft_fast_init_f32 (arm_rfft_fast_instance_f32 *S, uint16_t fftLen)
	Initialization function for the floating-point real FFT.
arm_status	arm_rfft_init_f32 (arm_rfft_instance_f32 *S, arm_cfft_radix4_instance_f32 *S_CFFT, uint32_t fftLenReal, uint32_t ifftFlagR, uint32_t bitReverseFlag)
	Initialization function for the floating-point RFFT/RIFFT.
arm_status	arm_rfft_init_q15 (arm_rfft_instance_q15 *S, uint32_t fftLenReal, uint32_t ifftFlagR, uint32_t bitReverseFlag)
	Initialization function for the Q15 RFFT/RIFFT.
arm_status	arm_rfft_init_q31 (arm_rfft_instance_q31 *S, uint32_t fftLenReal, uint32_t ifftFlagR, uint32_t bitReverseFlag)
	Initialization function for the Q31 RFFT/RIFFT.
void	arm_rfft_q15 (const arm_rfft_instance_q15 *S, q15_t *pSrc, q15_t *pDst)
	Processing function for the Q15 RFFT/RIFFT.
void	arm_rfft_q31 (const arm_rfft_instance_q31 *S, q31_t *pSrc, q31_t *pDst)
	Processing function for the Q31 RFFT/RIFFT.

Variables
static const float32_t	realCoefA [8192]
static const float32_t	realCoefB [8192]
static const q15_t ALIGN4	realCoefAQ15 [8192]
static const q15_t ALIGN4	realCoefBQ15 [8192]
static const q31_t	realCoefAQ31 [8192]
static const q31_t	realCoefBQ31 [8192]

Description

Function Documentation

void arm_rfft_f32	(	const arm_rfft_instance_f32 *	S,
		float32_t *	pSrc,
		float32_t *	pDst
	)

Deprecated:

Do not use this function. It has been superceded by arm_rfft_fast_f32 and will be removed in the future.

Parameters

[in]	*S	points to an instance of the floating-point RFFT/RIFFT structure.
[in]	*pSrc	points to the input buffer.
[out]	*pDst	points to the output buffer.

Returns

none.

References arm_bitreversal_f32(), arm_radix4_butterfly_f32(), arm_radix4_butterfly_inverse_f32(), arm_split_rfft_f32(), arm_split_rifft_f32(), arm_rfft_instance_f32::bitReverseFlagR, arm_cfft_radix4_instance_f32::bitRevFactor, arm_cfft_radix4_instance_f32::fftLen, arm_rfft_instance_f32::fftLenBy2, arm_rfft_instance_f32::ifftFlagR, arm_cfft_radix4_instance_f32::onebyfftLen, arm_cfft_radix4_instance_f32::pBitRevTable, arm_rfft_instance_f32::pCfft, arm_cfft_radix4_instance_f32::pTwiddle, arm_rfft_instance_f32::pTwiddleAReal, arm_rfft_instance_f32::pTwiddleBReal, arm_cfft_radix4_instance_f32::twidCoefModifier, and arm_rfft_instance_f32::twidCoefRModifier.

void arm_rfft_fast_f32	(	arm_rfft_fast_instance_f32 *	S,
		float32_t *	p,
		float32_t *	pOut,
		uint8_t	ifftFlag
	)

Parameters

[in]	*S	points to an arm_rfft_fast_instance_f32 structure.
[in]	*p	points to the input buffer.
[in]	*pOut	points to the output buffer.
[in]	ifftFlag	RFFT if flag is 0, RIFFT if flag is 1

Returns

none.

References arm_cfft_f32(), arm_cfft_instance_f32::fftLen, arm_rfft_fast_instance_f32::fftLenRFFT, merge_rfft_f32(), arm_rfft_fast_instance_f32::Sint, and stage_rfft_f32().

arm_status arm_rfft_fast_init_f32	(	arm_rfft_fast_instance_f32 *	S,
		uint16_t	fftLen
	)

Parameters

[in,out]	*S	points to an arm_rfft_fast_instance_f32 structure.
[in]	fftLen	length of the Real Sequence.

Returns

The function returns ARM_MATH_SUCCESS if initialization is successful or ARM_MATH_ARGUMENT_ERROR if fftLen is not a supported value.

Description:

The parameter fftLen Specifies length of RFFT/CIFFT process. Supported FFT Lengths are 32, 64, 128, 256, 512, 1024, 2048, 4096.

This Function also initializes Twiddle factor table pointer and Bit reversal table pointer.

References ARM_MATH_ARGUMENT_ERROR, ARM_MATH_SUCCESS, armBitRevIndexTable1024, ARMBITREVINDEXTABLE1024_TABLE_LENGTH, armBitRevIndexTable128, armBitRevIndexTable16, armBitRevIndexTable2048, ARMBITREVINDEXTABLE2048_TABLE_LENGTH, armBitRevIndexTable256, armBitRevIndexTable32, armBitRevIndexTable512, armBitRevIndexTable64, ARMBITREVINDEXTABLE_128_TABLE_LENGTH, ARMBITREVINDEXTABLE_256_TABLE_LENGTH, ARMBITREVINDEXTABLE_512_TABLE_LENGTH, ARMBITREVINDEXTABLE__16_TABLE_LENGTH, ARMBITREVINDEXTABLE__32_TABLE_LENGTH, ARMBITREVINDEXTABLE__64_TABLE_LENGTH, arm_cfft_instance_f32::bitRevLength, arm_cfft_instance_f32::fftLen, arm_rfft_fast_instance_f32::fftLenRFFT, arm_cfft_instance_f32::pBitRevTable, arm_cfft_instance_f32::pTwiddle, arm_rfft_fast_instance_f32::pTwiddleRFFT, arm_rfft_fast_instance_f32::Sint, status, twiddleCoef_1024, twiddleCoef_128, twiddleCoef_16, twiddleCoef_2048, twiddleCoef_256, twiddleCoef_32, twiddleCoef_512, twiddleCoef_64, twiddleCoef_rfft_1024, twiddleCoef_rfft_128, twiddleCoef_rfft_2048, twiddleCoef_rfft_256, twiddleCoef_rfft_32, twiddleCoef_rfft_4096, twiddleCoef_rfft_512, and twiddleCoef_rfft_64.

arm_status arm_rfft_init_f32	(	arm_rfft_instance_f32 *	S,
		arm_cfft_radix4_instance_f32 *	S_CFFT,
		uint32_t	fftLenReal,
		uint32_t	ifftFlagR,
		uint32_t	bitReverseFlag
	)

Deprecated:

Do not use this function. It has been superceded by arm_rfft_fast_init_f32 and will be removed in the future.

Parameters

[in,out]	*S	points to an instance of the floating-point RFFT/RIFFT structure.
[in,out]	*S_CFFT	points to an instance of the floating-point CFFT/CIFFT structure.
[in]	fftLenReal	length of the FFT.
[in]	ifftFlagR	flag that selects forward (ifftFlagR=0) or inverse (ifftFlagR=1) transform.
[in]	bitReverseFlag	flag that enables (bitReverseFlag=1) or disables (bitReverseFlag=0) bit reversal of output.

Returns

The function returns ARM_MATH_SUCCESS if initialization is successful or ARM_MATH_ARGUMENT_ERROR if fftLenReal is not a supported value.

Description:

The parameter fftLenReal Specifies length of RFFT/RIFFT Process. Supported FFT Lengths are 128, 512, 2048.

The parameter ifftFlagR controls whether a forward or inverse transform is computed. Set(=1) ifftFlagR to calculate RIFFT, otherwise RFFT is calculated.

The parameter bitReverseFlag controls whether output is in normal order or bit reversed order. Set(=1) bitReverseFlag for output to be in normal order otherwise output is in bit reversed order.

This function also initializes Twiddle factor table.

References arm_cfft_radix4_init_f32(), ARM_MATH_ARGUMENT_ERROR, ARM_MATH_SUCCESS, arm_rfft_instance_f32::bitReverseFlagR, arm_rfft_instance_f32::fftLenBy2, arm_rfft_instance_f32::fftLenReal, arm_rfft_instance_f32::ifftFlagR, arm_rfft_instance_f32::pCfft, arm_rfft_instance_f32::pTwiddleAReal, arm_rfft_instance_f32::pTwiddleBReal, realCoefA, realCoefB, status, and arm_rfft_instance_f32::twidCoefRModifier.

Referenced by arm_dct4_init_f32().

arm_status arm_rfft_init_q15	(	arm_rfft_instance_q15 *	S,
		uint32_t	fftLenReal,
		uint32_t	ifftFlagR,
		uint32_t	bitReverseFlag
	)

Parameters

[in,out]	*S	points to an instance of the Q15 RFFT/RIFFT structure.
[in]	fftLenReal	length of the FFT.
[in]	ifftFlagR	flag that selects forward (ifftFlagR=0) or inverse (ifftFlagR=1) transform.
[in]	bitReverseFlag	flag that enables (bitReverseFlag=1) or disables (bitReverseFlag=0) bit reversal of output.

Returns

The function returns ARM_MATH_SUCCESS if initialization is successful or ARM_MATH_ARGUMENT_ERROR if fftLenReal is not a supported value.

Description:

The parameter fftLenReal Specifies length of RFFT/RIFFT Process. Supported FFT Lengths are 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192.

The parameter ifftFlagR controls whether a forward or inverse transform is computed. Set(=1) ifftFlagR to calculate RIFFT, otherwise RFFT is calculated.

The parameter bitReverseFlag controls whether output is in normal order or bit reversed order. Set(=1) bitReverseFlag for output to be in normal order otherwise output is in bit reversed order.

This function also initializes Twiddle factor table.

References arm_cfft_sR_q15_len1024, arm_cfft_sR_q15_len128, arm_cfft_sR_q15_len16, arm_cfft_sR_q15_len2048, arm_cfft_sR_q15_len256, arm_cfft_sR_q15_len32, arm_cfft_sR_q15_len4096, arm_cfft_sR_q15_len512, arm_cfft_sR_q15_len64, ARM_MATH_ARGUMENT_ERROR, ARM_MATH_SUCCESS, arm_rfft_instance_q15::bitReverseFlagR, arm_rfft_instance_q15::fftLenReal, arm_rfft_instance_q15::ifftFlagR, arm_rfft_instance_q15::pCfft, arm_rfft_instance_q15::pTwiddleAReal, arm_rfft_instance_q15::pTwiddleBReal, realCoefAQ15, realCoefBQ15, status, and arm_rfft_instance_q15::twidCoefRModifier.

Referenced by arm_dct4_init_q15().

arm_status arm_rfft_init_q31	(	arm_rfft_instance_q31 *	S,
		uint32_t	fftLenReal,
		uint32_t	ifftFlagR,
		uint32_t	bitReverseFlag
	)

Parameters

[in,out]	*S	points to an instance of the Q31 RFFT/RIFFT structure.
[in]	fftLenReal	length of the FFT.
[in]	ifftFlagR	flag that selects forward (ifftFlagR=0) or inverse (ifftFlagR=1) transform.
[in]	bitReverseFlag	flag that enables (bitReverseFlag=1) or disables (bitReverseFlag=0) bit reversal of output.

Returns

The function returns ARM_MATH_SUCCESS if initialization is successful or ARM_MATH_ARGUMENT_ERROR if fftLenReal is not a supported value.

Description:

The parameter fftLenReal Specifies length of RFFT/RIFFT Process. Supported FFT Lengths are 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192.

The parameter ifftFlagR controls whether a forward or inverse transform is computed. Set(=1) ifftFlagR to calculate RIFFT, otherwise RFFT is calculated.

The parameter bitReverseFlag controls whether output is in normal order or bit reversed order. Set(=1) bitReverseFlag for output to be in normal order otherwise output is in bit reversed order.

7

This function also initializes Twiddle factor table.

References arm_cfft_sR_q31_len1024, arm_cfft_sR_q31_len128, arm_cfft_sR_q31_len16, arm_cfft_sR_q31_len2048, arm_cfft_sR_q31_len256, arm_cfft_sR_q31_len32, arm_cfft_sR_q31_len4096, arm_cfft_sR_q31_len512, arm_cfft_sR_q31_len64, ARM_MATH_ARGUMENT_ERROR, ARM_MATH_SUCCESS, arm_rfft_instance_q31::bitReverseFlagR, arm_rfft_instance_q31::fftLenReal, arm_rfft_instance_q31::ifftFlagR, arm_rfft_instance_q31::pCfft, arm_rfft_instance_q31::pTwiddleAReal, arm_rfft_instance_q31::pTwiddleBReal, realCoefAQ31, realCoefBQ31, status, and arm_rfft_instance_q31::twidCoefRModifier.

Referenced by arm_dct4_init_q31().

void arm_rfft_q15	(	const arm_rfft_instance_q15 *	S,
		q15_t *	pSrc,
		q15_t *	pDst
	)

Parameters

[in]	*S	points to an instance of the Q15 RFFT/RIFFT structure.
[in]	*pSrc	points to the input buffer.
[out]	*pDst	points to the output buffer.

Returns

none.

Input an output formats:

Internally input is downscaled by 2 for every stage to avoid saturations inside CFFT/CIFFT process. Hence the output format is different for different RFFT sizes. The input and output formats for different RFFT sizes and number of bits to upscale are mentioned in the tables below for RFFT and RIFFT:

Input and Output Formats for Q15 RFFT

Input and Output Formats for Q15 RIFFT

References arm_cfft_q15(), arm_split_rfft_q15(), arm_split_rifft_q15(), arm_rfft_instance_q15::bitReverseFlagR, arm_rfft_instance_q15::fftLenReal, arm_rfft_instance_q15::ifftFlagR, arm_rfft_instance_q15::pCfft, arm_rfft_instance_q15::pTwiddleAReal, arm_rfft_instance_q15::pTwiddleBReal, and arm_rfft_instance_q15::twidCoefRModifier.

void arm_rfft_q31	(	const arm_rfft_instance_q31 *	S,
		q31_t *	pSrc,
		q31_t *	pDst
	)

Parameters

[in]	*S	points to an instance of the Q31 RFFT/RIFFT structure.
[in]	*pSrc	points to the input buffer.
[out]	*pDst	points to the output buffer.

Returns

none.

Input an output formats:

Internally input is downscaled by 2 for every stage to avoid saturations inside CFFT/CIFFT process. Hence the output format is different for different RFFT sizes. The input and output formats for different RFFT sizes and number of bits to upscale are mentioned in the tables below for RFFT and RIFFT:

Input and Output Formats for Q31 RFFT

Input and Output Formats for Q31 RIFFT

References arm_cfft_q31(), arm_split_rfft_q31(), arm_split_rifft_q31(), arm_rfft_instance_q31::bitReverseFlagR, arm_rfft_instance_q31::fftLenReal, arm_rfft_instance_q31::ifftFlagR, arm_rfft_instance_q31::pCfft, arm_rfft_instance_q31::pTwiddleAReal, arm_rfft_instance_q31::pTwiddleBReal, and arm_rfft_instance_q31::twidCoefRModifier.

Referenced by arm_dct4_q31().

Variable Documentation

const float32_t realCoefA[8192]

static

Generation of realCoefA array:

n = 4096

for (i = 0; i < n; i++)    
 {    
   pATable[2 * i] = 0.5 * (1.0 - sin (2 * PI / (double) (2 * n) * (double) i));    
   pATable[2 * i + 1] = 0.5 * (-1.0 * cos (2 * PI / (double) (2 * n) * (double) i));    
 } 

Referenced by arm_rfft_init_f32().

const q15_t ALIGN4 realCoefAQ15[8192]

static

Generation fixed-point realCoefAQ15 array in Q15 format:

n = 4096

for (i = 0; i < n; i++)    
 {    
   pATable[2 * i] = 0.5 * (1.0 - sin (2 * PI / (double) (2 * n) * (double) i));    
   pATable[2 * i + 1] = 0.5 * (-1.0 * cos (2 * PI / (double) (2 * n) * (double) i));    
 } 

Convert to fixed point Q15 format round(pATable[i] * pow(2, 15))

Referenced by arm_rfft_init_q15().

const q31_t realCoefAQ31[8192]

static

Generation fixed-point realCoefAQ31 array in Q31 format:

n = 4096

for (i = 0; i < n; i++)    
{    
   pATable[2 * i] = 0.5 * (1.0 - sin (2 * PI / (double) (2 * n) * (double) i));    
   pATable[2 * i + 1] = 0.5 * (-1.0 * cos (2 * PI / (double) (2 * n) * (double) i));    
}

Convert to fixed point Q31 format round(pATable[i] * pow(2, 31))

Referenced by arm_rfft_init_q31().

const float32_t realCoefB[8192]

static

Generation of realCoefB array:

n = 4096

for (i = 0; i < n; i++)    
{    
   pBTable[2 * i] = 0.5 * (1.0 + sin (2 * PI / (double) (2 * n) * (double) i));    
   pBTable[2 * i + 1] = 0.5 * (1.0 * cos (2 * PI / (double) (2 * n) * (double) i));    
 } 

Referenced by arm_rfft_init_f32().

const q15_t ALIGN4 realCoefBQ15[8192]

static

Generation of real_CoefB array:

n = 4096

for (i = 0; i < n; i++)    
 {    
   pBTable[2 * i] = 0.5 * (1.0 + sin (2 * PI / (double) (2 * n) * (double) i));    
   pBTable[2 * i + 1] = 0.5 * (1.0 * cos (2 * PI / (double) (2 * n) * (double) i));    
 } 

Convert to fixed point Q15 format round(pBTable[i] * pow(2, 15))

Referenced by arm_rfft_init_q15().

const q31_t realCoefBQ31[8192]

static

Generation of realCoefBQ31 array:

n = 4096

for (i = 0; i < n; i++)    
{    
   pBTable[2 * i] = 0.5 * (1.0 + sin (2 * PI / (double) (2 * n) * (double) i));    
   pBTable[2 * i + 1] = 0.5 * (1.0 * cos (2 * PI / (double) (2 * n) * (double) i));    
} 

Convert to fixed point Q31 format round(pBTable[i] * pow(2, 31))

Referenced by arm_rfft_init_q31().