read_me.txt

IDCT 反离散余弦变换原程序

File Name:       idct_122700.zip

File Contents:   read_me.txt
                 mds_def.h
                 r8x8invdct.asm
                 tr8x8invdct.c
                 tr8x8invdct.h

Module Name:     The implementation of Inverse DCT for 8x8 real data.
Label Name:      __r8x8invdct
Description:     This is the implementation of Chen's algorithm of IDCT.
                 It is based on the separable nature of IDCT for multi-
                 dimension. The input matrix is 8x8 real data. First, one dime-
                 sional 8-point IDCT is calculated for each of the 8 rows. The
                 output is stored in a separate matrix after transpose. Then again 
                 8-point IDCT is calculated on each row of matrix. The output
                 is again stored in a transpose matrix. This is final output.
				 
                 Chen's algorithm has 4 stages (parts) of implementation.

                 This implementation works only for 8x8 input. The input data 
                 should be real. The range of input should be -256 to 255. 
				 
                 The algorithm is in-placed. 
                 The prototype of the C callable is as follows:

                 _r8x8dct(fract16 *in, fract16 *coeff, fract16 *temp);

                   *in -> Pointer to Input vector.
                   *coeff -> Pointer to coefficients.
                   *temp -> Pointer to temproary data. 

           Note: The algorithm reads the input data from the "in" matrix.  
                 First 8-point IDCT will be calculated for all the 8 rows.
                 This output is stored in "temp" buffer in the transposed 
                 form at bit reversed locations. 
                 Again the 8-point IDCT is applied on all the 8 rows of 
                 "temp" buffer. Final output computed is stored in "in" 
                 buffer in transposed form at bit reversed locations.
                 The operation of transposing the matrix and calculation of
                 bit reversed are carried out while writing the data without
                 any explicit code.

                 Output of function is provided "in" buffer in normal order.

Registers Used:      R0, R1, R2, R3, R4, R5, R6, R7, P0, P1, P2, P3, P4, P5, A0, A1.
Other Register Used: I0, I1, I2, I3, B0, B2, B3, M0, M1, M2, L3 registers and LC0.

Performance: (Timer version 0.6.33)

                 Code Size : 344 Bytes.

                 Memory Required :
                   Input Matrix:     8 * 8 * 2 Bytes.
                   Coefficients:     16 Bytes
                   Temporary Matrix: 8 * 8 * 2 Bytes
	
                 Cycle Count :

                 -----------------------------------------
                 |  Size  |  Forward DCT  |  Inverse DCT |
                 -----------------------------------------
                 |  8x8   |   284 Cycles  |  311 Cycles  |
                 -----------------------------------------