Diff: src/Cortex-M4-M3/TransformFunctions/arm_dct4_q31.c

Revision:

0:1014af42efd9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Cortex-M4-M3/TransformFunctions/arm_dct4_q31.c	Thu Mar 10 15:07:50 2011 +0000
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+/* ----------------------------------------------------------------------  
+* Copyright (C) 2010 ARM Limited. All rights reserved.  
+*  
+* $Date:        29. November 2010  
+* $Revision: 	V1.0.3  
+*  
+* Project: 	    CMSIS DSP Library  
+* Title:	    arm_dct4_q31.c  
+*  
+* Description:	Processing function of DCT4 & IDCT4 Q31.  
+*  
+* Target Processor: Cortex-M4/Cortex-M3
+*  
+* Version 1.0.3 2010/11/29 
+*    Re-organized the CMSIS folders and updated documentation.  
+*   
+* Version 1.0.2 2010/11/11  
+*    Documentation updated.   
+*  
+* Version 1.0.1 2010/10/05   
+*    Production release and review comments incorporated.  
+*  
+* Version 1.0.0 2010/09/20   
+*    Production release and review comments incorporated.  
+* -------------------------------------------------------------------- */ 
+ 
+#include "arm_math.h" 
+ 
+/**  
+ * @addtogroup DCT4_IDCT4  
+ * @{  
+ */ 
+ 
+/**  
+ * @brief Processing function for the Q31 DCT4/IDCT4. 
+ * @param[in]       *S             points to an instance of the Q31 DCT4 structure. 
+ * @param[in]       *pState        points to state buffer. 
+ * @param[in,out]   *pInlineBuffer points to the in-place input and output buffer. 
+ * @return none. 
+ * \par Input an output formats:  
+ * Input samples need to be downscaled by 1 bit to avoid saturations in the Q31 DCT process,  
+ * as the conversion from DCT2 to DCT4 involves one subtraction.  
+ * 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:   
+ *  
+ * \image html dct4FormatsQ31Table.gif  
+ */ 
+ 
+void arm_dct4_q31( 
+  const arm_dct4_instance_q31 * S, 
+  q31_t * pState, 
+  q31_t * pInlineBuffer) 
+{ 
+  uint16_t i;                                    /* Loop counter */ 
+  q31_t *weights = S->pTwiddle;                  /* Pointer to the Weights table */ 
+  q31_t *cosFact = S->pCosFactor;                /* Pointer to the cos factors table */ 
+  q31_t *pS1, *pS2, *pbuff;                      /* Temporary pointers for input buffer and pState buffer */ 
+  q31_t in;                                      /* Temporary variable */ 
+ 
+ 
+  /* DCT4 computation involves DCT2 (which is calculated using RFFT)  
+   * along with some pre-processing and post-processing.  
+   * Computational procedure is explained as follows:  
+   * (a) Pre-processing involves multiplying input with cos factor,  
+   *     r(n) = 2 * u(n) * cos(pi*(2*n+1)/(4*n))  
+   *              where,  
+   *                 r(n) -- output of preprocessing  
+   *                 u(n) -- input to preprocessing(actual Source buffer)  
+   * (b) Calculation of DCT2 using FFT is divided into three steps:  
+   *                  Step1: Re-ordering of even and odd elements of input.  
+   *                  Step2: Calculating FFT of the re-ordered input.  
+   *                  Step3: Taking the real part of the product of FFT output and weights.  
+   * (c) Post-processing - DCT4 can be obtained from DCT2 output using the following equation:  
+   *                   Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)  
+   *                        where,  
+   *                           Y4 -- DCT4 output,   Y2 -- DCT2 output  
+   * (d) Multiplying the output with the normalizing factor sqrt(2/N).  
+   */ 
+ 
+        /*-------- Pre-processing ------------*/ 
+  /* Multiplying input with cos factor i.e. r(n) = 2 * x(n) * cos(pi*(2*n+1)/(4*n)) */ 
+  arm_mult_q31(pInlineBuffer, cosFact, pInlineBuffer, S->N); 
+  arm_shift_q31(pInlineBuffer, 1, pInlineBuffer, S->N); 
+ 
+  /* ----------------------------------------------------------------  
+   * Step1: Re-ordering of even and odd elements as  
+   *             pState[i] =  pInlineBuffer[2*i] and  
+   *             pState[N-i-1] = pInlineBuffer[2*i+1] where i = 0 to N/2  
+   ---------------------------------------------------------------------*/ 
+ 
+  /* pS1 initialized to pState */ 
+  pS1 = pState; 
+ 
+  /* pS2 initialized to pState+N-1, so that it points to the end of the state buffer */ 
+  pS2 = pState + (S->N - 1u); 
+ 
+  /* pbuff initialized to input buffer */ 
+  pbuff = pInlineBuffer; 
+ 
+  /* Initializing the loop counter to N/2 >> 2 for loop unrolling by 4 */ 
+  i = S->Nby2 >> 2u; 
+ 
+  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
+   ** a second loop below computes the remaining 1 to 3 samples. */ 
+  do 
+  { 
+    /* Re-ordering of even and odd elements */ 
+    /* pState[i] =  pInlineBuffer[2*i] */ 
+    *pS1++ = *pbuff++; 
+    /* pState[N-i-1] = pInlineBuffer[2*i+1] */ 
+    *pS2-- = *pbuff++; 
+ 
+    *pS1++ = *pbuff++; 
+    *pS2-- = *pbuff++; 
+ 
+    *pS1++ = *pbuff++; 
+    *pS2-- = *pbuff++; 
+ 
+    *pS1++ = *pbuff++; 
+    *pS2-- = *pbuff++; 
+ 
+    /* Decrement the loop counter */ 
+    i--; 
+  } while(i > 0u); 
+ 
+  /* pbuff initialized to input buffer */ 
+  pbuff = pInlineBuffer; 
+ 
+  /* pS1 initialized to pState */ 
+  pS1 = pState; 
+ 
+  /* Initializing the loop counter to N/4 instead of N for loop unrolling */ 
+  i = S->N >> 2u; 
+ 
+  /* Processing with loop unrolling 4 times as N is always multiple of 4.  
+   * Compute 4 outputs at a time */ 
+  do 
+  { 
+    /* Writing the re-ordered output back to inplace input buffer */ 
+    *pbuff++ = *pS1++; 
+    *pbuff++ = *pS1++; 
+    *pbuff++ = *pS1++; 
+    *pbuff++ = *pS1++; 
+ 
+    /* Decrement the loop counter */ 
+    i--; 
+  } while(i > 0u); 
+ 
+ 
+  /* ---------------------------------------------------------  
+   *     Step2: Calculate RFFT for N-point input  
+   * ---------------------------------------------------------- */ 
+  /* pInlineBuffer is real input of length N , pState is the complex output of length 2N */ 
+  arm_rfft_q31(S->pRfft, pInlineBuffer, pState); 
+ 
+  /*----------------------------------------------------------------------  
+   *  Step3: Multiply the FFT output with the weights.  
+   *----------------------------------------------------------------------*/ 
+  arm_cmplx_mult_cmplx_q31(pState, weights, pState, S->N); 
+ 
+  /* The output of complex multiplication is in 3.29 format.  
+   * Hence changing the format of N (i.e. 2*N elements) complex numbers to 1.31 format by shifting left by 2 bits. */ 
+  arm_shift_q31(pState, 2, pState, S->N * 2); 
+ 
+  /* ----------- Post-processing ---------- */ 
+  /* DCT-IV can be obtained from DCT-II by the equation,  
+   *       Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)  
+   *       Hence, Y4(0) = Y2(0)/2  */ 
+  /* Getting only real part from the output and Converting to DCT-IV */ 
+ 
+  /* Initializing the loop counter to N >> 2 for loop unrolling by 4 */ 
+  i = (S->N - 1u) >> 2u; 
+ 
+  /* pbuff initialized to input buffer. */ 
+  pbuff = pInlineBuffer; 
+ 
+  /* pS1 initialized to pState */ 
+  pS1 = pState; 
+ 
+  /* Calculating Y4(0) from Y2(0) using Y4(0) = Y2(0)/2 */ 
+  in = *pS1++ >> 1u; 
+  /* input buffer acts as inplace, so output values are stored in the input itself. */ 
+  *pbuff++ = in; 
+ 
+  /* pState pointer is incremented twice as the real values are located alternatively in the array */ 
+  pS1++; 
+ 
+  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
+   ** a second loop below computes the remaining 1 to 3 samples. */ 
+  do 
+  { 
+    /* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */ 
+    /* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */ 
+    in = *pS1++ - in; 
+    *pbuff++ = in; 
+    /* points to the next real value */ 
+    pS1++; 
+ 
+    in = *pS1++ - in; 
+    *pbuff++ = in; 
+    pS1++; 
+ 
+    in = *pS1++ - in; 
+    *pbuff++ = in; 
+    pS1++; 
+ 
+    in = *pS1++ - in; 
+    *pbuff++ = in; 
+    pS1++; 
+ 
+    /* Decrement the loop counter */ 
+    i--; 
+  } while(i > 0u); 
+ 
+  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
+   ** No loop unrolling is used. */ 
+  i = (S->N - 1u) % 0x4u; 
+ 
+  while(i > 0u) 
+  { 
+    /* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */ 
+    /* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */ 
+    in = *pS1++ - in; 
+    *pbuff++ = in; 
+    /* points to the next real value */ 
+    pS1++; 
+ 
+    /* Decrement the loop counter */ 
+    i--; 
+  } 
+ 
+ 
+        /*------------ Normalizing the output by multiplying with the normalizing factor ----------*/ 
+ 
+  /* Initializing the loop counter to N/4 instead of N for loop unrolling */ 
+  i = S->N >> 2u; 
+ 
+  /* pbuff initialized to the pInlineBuffer(now contains the output values) */ 
+  pbuff = pInlineBuffer; 
+ 
+  /* Processing with loop unrolling 4 times as N is always multiple of 4.  Compute 4 outputs at a time */ 
+  do 
+  { 
+    /* Multiplying pInlineBuffer with the normalizing factor sqrt(2/N) */ 
+    in = *pbuff; 
+    *pbuff++ = ((q31_t) (((q63_t) in * S->normalize) >> 31)); 
+ 
+    in = *pbuff; 
+    *pbuff++ = ((q31_t) (((q63_t) in * S->normalize) >> 31)); 
+ 
+    in = *pbuff; 
+    *pbuff++ = ((q31_t) (((q63_t) in * S->normalize) >> 31)); 
+ 
+    in = *pbuff; 
+    *pbuff++ = ((q31_t) (((q63_t) in * S->normalize) >> 31)); 
+ 
+    /* Decrement the loop counter */ 
+    i--; 
+  } while(i > 0u); 
+ 
+} 
+ 
+/**  
+   * @} end of DCT4_IDCT4 group  
+   */