📄 img_histogram.h64
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;* ======================================================================== *;
;* TEXAS INSTRUMENTS, INC. *;
;* *;
;* IMGLIB DSP Image/Video Processing Library *;
;* *;
;* Release: Revision 1.04b *;
;* CVS Revision: 1.8 Sun Sep 29 03:32:23 2002 (UTC) *;
;* Snapshot date: 23-Oct-2003 *;
;* *;
;* This library contains proprietary intellectual property of Texas *;
;* Instruments, Inc. The library and its source code are protected by *;
;* various copyrights, and portions may also be protected by patents or *;
;* other legal protections. *;
;* *;
;* This software is licensed for use with Texas Instruments TMS320 *;
;* family DSPs. This license was provided to you prior to installing *;
;* the software. You may review this license by consulting the file *;
;* TI_license.PDF which accompanies the files in this library. *;
;* ------------------------------------------------------------------------ *;
;* Copyright (C) 2003 Texas Instruments, Incorporated. *;
;* All Rights Reserved. *;
;* ======================================================================== *;
;* ======================================================================== *;
;* Assembler compatibility shim for assembling 4.30 and later code on *;
;* tools prior to 4.30. *;
;* ======================================================================== *;
;* ======================================================================== *;
;* End of assembler compatibility shim. *;
;* ======================================================================== *;
* ========================================================================= *
* TEXAS INSTRUMENTS, INC. *
* *
* NAME *
* IMG_histogram *
* *
* REVISION DATE *
* 26-May-2000 *
* *
* USAGE *
* This routine is C-callable and can be called as: *
* *
* void IMG_histogram *
* ( *
* const unsigned char *restrict img, /* incoming image */ *
* int n, /* number of pixels */ *
* short accumulate, /* weighting factor */ *
* short *restrict t_hist, /* temporary array */ *
* short *restrict hist /* IMG_histogram. */ *
* ); *
* *
* *
* DESCRIPTION *
* This code takes a IMG_histogram of an array of n, 8 bit inputs. It *
* returns the IMG_histogram of 256 bins at 16 bit precision. It can *
* either add or subtract to an existing IMG_histogram, using the *
* 'accumulate' control. *
* *
* It requires some temporary storage for 4 temporary histograms, *
* which are later summed together. *
* *
* void IMG_histogram *
* ( *
* const unsigned char *restrict img, /* incoming image */ *
* int n, /* number of pixels */ *
* short accumulate, /* weighting factor */ *
* short *restrict t_hist, /* temporary array */ *
* short *restrict hist /* IMG_histogram. */ *
* ) *
* { *
* int pixel, j; *
* for (j = 0; j < n; j++) *
* { *
* pixel = (int) img[j]; *
* hist[pixel] += accumulate; *
* } *
* } *
* *
* The above C code is a general implementation without *
* restrictions. The assembly code has various restrictions, as *
* noted below. *
* *
* ASSUMPTIONS *
* It is assumed that the temporary array of data, t_hist is *
* initialised to zero. The input array of image data must be *
* aligned to a 4 byte boundary and n must be a multiple of 8. The *
* maximum number of pixels that can be profiled in each bin is *
* 65535 in the main IMG_histogram. *
* *
* MEMORY NOTE *
* No bank conflicts occur. *
* *
* The main IMG_histogram loop accesses two banks on 8 of 9 cycles, *
* and four banks on the 9th cycle. The summing loop accesses *
* 128 bits every cycle. *
* *
* TECHNIQUES *
* This code operates on four interleaved IMG_histogram bins. The loop *
* is divided into two halves: The "even" half operates on the *
* even-numbered words from the input image, and the "odd" half *
* operates on odd words. Each half processes four pixels at a *
* time, and both halves operate on the same four sets of IMG_histogram *
* bins. This introduces a memory dependency on the IMG_histogram bins *
* which ordinarily would degrade performance. To break the memory *
* depenencies, the two halves forward their results to each other *
* via the register file, bypassing memory. *
* *
* Exact memory access ordering obviates the need to predicate *
* stores The algorithm is ordered as follows: *
* *
* 1. Load from IMG_histogram for even half *
* 2. Store odd_bin to IMG_histogram for odd half (previous itn.) *
* 3. if data_even == previous data_odd increment even_bin by 2 *
* else increment even_bin by 1, forward to odd *
* 4. Load from IMG_histogram for odd half (current itn.) *
* 5. Store even_bin to IMG_histogram for even half *
* 6. if data_odd == previous data_even increment odd_bin by 2 *
* else increment odd_bin by 1, forward to even *
* 7. goto 1. *
* *
* With this particular ordering, forwarding is necessary between *
* even/odd halves when pixels in adjacent halves need to be *
* placed in the same bin. *
* *
* The store is never predicated and occurs speculatively *
* as it will be overwritten by the next value containing the *
* extra forwarded value. *
* *
* The four histograms are interleaved with each bin spaced four *
* half-words apart and each IMG_histogram starting in a different *
* memory bank. This allows the four IMG_histogram accesses to proceed *
* in any order without worrying about bank conflicts. The *
* diagram below illustrates this: (addresses are halfword *
* offsets) *
* *
* 0 1 2 3 4 5 6 ... *
* | hst 0 | hst 1 | hst 2 | hst 3 | hst 0 | hst 1 | ... ... *
* | bin 0 | bin 0 | bin 0 | bin 0 | bin 1 | bin 1 | ... ... *
* *
* These are then summed together at the end in blocks of 4 *
* *
* CYCLES *
* 9 * n/8 + 228 *
* *
* CODESIZE *
* 552 bytes *
* *
* ------------------------------------------------------------------------- *
* Copyright (c) 2003 Texas Instruments, Incorporated. *
* All Rights Reserved. *
* ========================================================================= *
.global _IMG_histogram
* ========================================================================= *
* End of file: img_histogram.h64 *
* ------------------------------------------------------------------------- *
* Copyright (c) 2003 Texas Instruments, Incorporated. *
* All Rights Reserved. *
* ========================================================================= *
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