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jidctint-neon.c
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/*
* jidctint-neon.c - accurate integer IDCT (Arm Neon)
*
* Copyright (C) 2020, Arm Limited. All Rights Reserved.
* Copyright (C) 2020, D. R. Commander. All Rights Reserved.
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
*
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
*
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/
#define JPEG_INTERNALS
#include "jconfigint.h"
#include "../../jinclude.h"
#include "../../jpeglib.h"
#include "../../jsimd.h"
#include "../../jdct.h"
#include "../../jsimddct.h"
#include "../jsimd.h"
#include "align.h"
#include "neon-compat.h"
#include <arm_neon.h>
#define CONST_BITS 13
#define PASS1_BITS 2
#define DESCALE_P1 (CONST_BITS - PASS1_BITS)
#define DESCALE_P2 (CONST_BITS + PASS1_BITS + 3)
/* The computation of the inverse DCT requires the use of constants known at
* compile time. Scaled integer constants are used to avoid floating-point
* arithmetic:
* 0.298631336 = 2446 * 2^-13
* 0.390180644 = 3196 * 2^-13
* 0.541196100 = 4433 * 2^-13
* 0.765366865 = 6270 * 2^-13
* 0.899976223 = 7373 * 2^-13
* 1.175875602 = 9633 * 2^-13
* 1.501321110 = 12299 * 2^-13
* 1.847759065 = 15137 * 2^-13
* 1.961570560 = 16069 * 2^-13
* 2.053119869 = 16819 * 2^-13
* 2.562915447 = 20995 * 2^-13
* 3.072711026 = 25172 * 2^-13
*/
#define F_0_298 2446
#define F_0_390 3196
#define F_0_541 4433
#define F_0_765 6270
#define F_0_899 7373
#define F_1_175 9633
#define F_1_501 12299
#define F_1_847 15137
#define F_1_961 16069
#define F_2_053 16819
#define F_2_562 20995
#define F_3_072 25172
#define F_1_175_MINUS_1_961 (F_1_175 - F_1_961)
#define F_1_175_MINUS_0_390 (F_1_175 - F_0_390)
#define F_0_541_MINUS_1_847 (F_0_541 - F_1_847)
#define F_3_072_MINUS_2_562 (F_3_072 - F_2_562)
#define F_0_298_MINUS_0_899 (F_0_298 - F_0_899)
#define F_1_501_MINUS_0_899 (F_1_501 - F_0_899)
#define F_2_053_MINUS_2_562 (F_2_053 - F_2_562)
#define F_0_541_PLUS_0_765 (F_0_541 + F_0_765)
ALIGN(16) static const int16_t jsimd_idct_islow_neon_consts[] = {
F_0_899, F_0_541,
F_2_562, F_0_298_MINUS_0_899,
F_1_501_MINUS_0_899, F_2_053_MINUS_2_562,
F_0_541_PLUS_0_765, F_1_175,
F_1_175_MINUS_0_390, F_0_541_MINUS_1_847,
F_3_072_MINUS_2_562, F_1_175_MINUS_1_961,
0, 0, 0, 0
};
/* Forward declaration of regular and sparse IDCT helper functions */
static INLINE void jsimd_idct_islow_pass1_regular(int16x4_t row0,
int16x4_t row1,
int16x4_t row2,
int16x4_t row3,
int16x4_t row4,
int16x4_t row5,
int16x4_t row6,
int16x4_t row7,
int16x4_t quant_row0,
int16x4_t quant_row1,
int16x4_t quant_row2,
int16x4_t quant_row3,
int16x4_t quant_row4,
int16x4_t quant_row5,
int16x4_t quant_row6,
int16x4_t quant_row7,
int16_t *workspace_1,
int16_t *workspace_2);
static INLINE void jsimd_idct_islow_pass1_sparse(int16x4_t row0,
int16x4_t row1,
int16x4_t row2,
int16x4_t row3,
int16x4_t quant_row0,
int16x4_t quant_row1,
int16x4_t quant_row2,
int16x4_t quant_row3,
int16_t *workspace_1,
int16_t *workspace_2);
static INLINE void jsimd_idct_islow_pass2_regular(int16_t *workspace,
JSAMPARRAY output_buf,
JDIMENSION output_col,
unsigned buf_offset);
static INLINE void jsimd_idct_islow_pass2_sparse(int16_t *workspace,
JSAMPARRAY output_buf,
JDIMENSION output_col,
unsigned buf_offset);
/* Perform dequantization and inverse DCT on one block of coefficients. For
* reference, the C implementation (jpeg_idct_slow()) can be found in
* jidctint.c.
*
* Optimization techniques used for fast data access:
*
* In each pass, the inverse DCT is computed for the left and right 4x8 halves
* of the DCT block. This avoids spilling due to register pressure, and the
* increased granularity allows for an optimized calculation depending on the
* values of the DCT coefficients. Between passes, intermediate data is stored
* in 4x8 workspace buffers.
*
* Transposing the 8x8 DCT block after each pass can be achieved by transposing
* each of the four 4x4 quadrants and swapping quadrants 1 and 2 (refer to the
* diagram below.) Swapping quadrants is cheap, since the second pass can just
* swap the workspace buffer pointers.
*
* +-------+-------+ +-------+-------+
* | | | | | |
* | 0 | 1 | | 0 | 2 |
* | | | transpose | | |
* +-------+-------+ ------> +-------+-------+
* | | | | | |
* | 2 | 3 | | 1 | 3 |
* | | | | | |
* +-------+-------+ +-------+-------+
*
* Optimization techniques used to accelerate the inverse DCT calculation:
*
* In a DCT coefficient block, the coefficients are increasingly likely to be 0
* as you move diagonally from top left to bottom right. If whole rows of
* coefficients are 0, then the inverse DCT calculation can be simplified. On
* the first pass of the inverse DCT, we test for three special cases before
* defaulting to a full "regular" inverse DCT:
*
* 1) Coefficients in rows 4-7 are all zero. In this case, we perform a
* "sparse" simplified inverse DCT on rows 0-3.
* 2) AC coefficients (rows 1-7) are all zero. In this case, the inverse DCT
* result is equal to the dequantized DC coefficients.
* 3) AC and DC coefficients are all zero. In this case, the inverse DCT
* result is all zero. For the left 4x8 half, this is handled identically
* to Case 2 above. For the right 4x8 half, we do no work and signal that
* the "sparse" algorithm is required for the second pass.
*
* In the second pass, only a single special case is tested: whether the AC and
* DC coefficients were all zero in the right 4x8 block during the first pass
* (refer to Case 3 above.) If this is the case, then a "sparse" variant of
* the second pass is performed for both the left and right halves of the DCT
* block. (The transposition after the first pass means that the right 4x8
* block during the first pass becomes rows 4-7 during the second pass.)
*/
void jsimd_idct_islow_neon(void *dct_table, JCOEFPTR coef_block,
JSAMPARRAY output_buf, JDIMENSION output_col)
{
ISLOW_MULT_TYPE *quantptr = dct_table;
int16_t workspace_l[8 * DCTSIZE / 2];
int16_t workspace_r[8 * DCTSIZE / 2];
/* Compute IDCT first pass on left 4x8 coefficient block. */
/* Load DCT coefficients in left 4x8 block. */
int16x4_t row0 = vld1_s16(coef_block + 0 * DCTSIZE);
int16x4_t row1 = vld1_s16(coef_block + 1 * DCTSIZE);
int16x4_t row2 = vld1_s16(coef_block + 2 * DCTSIZE);
int16x4_t row3 = vld1_s16(coef_block + 3 * DCTSIZE);
int16x4_t row4 = vld1_s16(coef_block + 4 * DCTSIZE);
int16x4_t row5 = vld1_s16(coef_block + 5 * DCTSIZE);
int16x4_t row6 = vld1_s16(coef_block + 6 * DCTSIZE);
int16x4_t row7 = vld1_s16(coef_block + 7 * DCTSIZE);
/* Load quantization table for left 4x8 block. */
int16x4_t quant_row0 = vld1_s16(quantptr + 0 * DCTSIZE);
int16x4_t quant_row1 = vld1_s16(quantptr + 1 * DCTSIZE);
int16x4_t quant_row2 = vld1_s16(quantptr + 2 * DCTSIZE);
int16x4_t quant_row3 = vld1_s16(quantptr + 3 * DCTSIZE);
int16x4_t quant_row4 = vld1_s16(quantptr + 4 * DCTSIZE);
int16x4_t quant_row5 = vld1_s16(quantptr + 5 * DCTSIZE);
int16x4_t quant_row6 = vld1_s16(quantptr + 6 * DCTSIZE);
int16x4_t quant_row7 = vld1_s16(quantptr + 7 * DCTSIZE);
/* Construct bitmap to test if DCT coefficients in left 4x8 block are 0. */
int16x4_t bitmap = vorr_s16(row7, row6);
bitmap = vorr_s16(bitmap, row5);
bitmap = vorr_s16(bitmap, row4);
int64_t bitmap_rows_4567 = vget_lane_s64(vreinterpret_s64_s16(bitmap), 0);
if (bitmap_rows_4567 == 0) {
bitmap = vorr_s16(bitmap, row3);
bitmap = vorr_s16(bitmap, row2);
bitmap = vorr_s16(bitmap, row1);
int64_t left_ac_bitmap = vget_lane_s64(vreinterpret_s64_s16(bitmap), 0);
if (left_ac_bitmap == 0) {
int16x4_t dcval = vshl_n_s16(vmul_s16(row0, quant_row0), PASS1_BITS);
int16x4x4_t quadrant = { { dcval, dcval, dcval, dcval } };
/* Store 4x4 blocks to workspace, transposing in the process. */
vst4_s16(workspace_l, quadrant);
vst4_s16(workspace_r, quadrant);
} else {
jsimd_idct_islow_pass1_sparse(row0, row1, row2, row3, quant_row0,
quant_row1, quant_row2, quant_row3,
workspace_l, workspace_r);
}
} else {
jsimd_idct_islow_pass1_regular(row0, row1, row2, row3, row4, row5,
row6, row7, quant_row0, quant_row1,
quant_row2, quant_row3, quant_row4,
quant_row5, quant_row6, quant_row7,
workspace_l, workspace_r);
}
/* Compute IDCT first pass on right 4x8 coefficient block. */
/* Load DCT coefficients in right 4x8 block. */
row0 = vld1_s16(coef_block + 0 * DCTSIZE + 4);
row1 = vld1_s16(coef_block + 1 * DCTSIZE + 4);
row2 = vld1_s16(coef_block + 2 * DCTSIZE + 4);
row3 = vld1_s16(coef_block + 3 * DCTSIZE + 4);
row4 = vld1_s16(coef_block + 4 * DCTSIZE + 4);
row5 = vld1_s16(coef_block + 5 * DCTSIZE + 4);
row6 = vld1_s16(coef_block + 6 * DCTSIZE + 4);
row7 = vld1_s16(coef_block + 7 * DCTSIZE + 4);
/* Load quantization table for right 4x8 block. */
quant_row0 = vld1_s16(quantptr + 0 * DCTSIZE + 4);
quant_row1 = vld1_s16(quantptr + 1 * DCTSIZE + 4);
quant_row2 = vld1_s16(quantptr + 2 * DCTSIZE + 4);
quant_row3 = vld1_s16(quantptr + 3 * DCTSIZE + 4);
quant_row4 = vld1_s16(quantptr + 4 * DCTSIZE + 4);
quant_row5 = vld1_s16(quantptr + 5 * DCTSIZE + 4);
quant_row6 = vld1_s16(quantptr + 6 * DCTSIZE + 4);
quant_row7 = vld1_s16(quantptr + 7 * DCTSIZE + 4);
/* Construct bitmap to test if DCT coefficients in right 4x8 block are 0. */
bitmap = vorr_s16(row7, row6);
bitmap = vorr_s16(bitmap, row5);
bitmap = vorr_s16(bitmap, row4);
bitmap_rows_4567 = vget_lane_s64(vreinterpret_s64_s16(bitmap), 0);
bitmap = vorr_s16(bitmap, row3);
bitmap = vorr_s16(bitmap, row2);
bitmap = vorr_s16(bitmap, row1);
int64_t right_ac_bitmap = vget_lane_s64(vreinterpret_s64_s16(bitmap), 0);
/* If this remains non-zero, a "regular" second pass will be performed. */
int64_t right_ac_dc_bitmap = 1;
if (right_ac_bitmap == 0) {
bitmap = vorr_s16(bitmap, row0);
right_ac_dc_bitmap = vget_lane_s64(vreinterpret_s64_s16(bitmap), 0);
if (right_ac_dc_bitmap != 0) {
int16x4_t dcval = vshl_n_s16(vmul_s16(row0, quant_row0), PASS1_BITS);
int16x4x4_t quadrant = { { dcval, dcval, dcval, dcval } };
/* Store 4x4 blocks to workspace, transposing in the process. */
vst4_s16(workspace_l + 4 * DCTSIZE / 2, quadrant);
vst4_s16(workspace_r + 4 * DCTSIZE / 2, quadrant);
}
} else {
if (bitmap_rows_4567 == 0) {
jsimd_idct_islow_pass1_sparse(row0, row1, row2, row3, quant_row0,
quant_row1, quant_row2, quant_row3,
workspace_l + 4 * DCTSIZE / 2,
workspace_r + 4 * DCTSIZE / 2);
} else {
jsimd_idct_islow_pass1_regular(row0, row1, row2, row3, row4, row5,
row6, row7, quant_row0, quant_row1,
quant_row2, quant_row3, quant_row4,
quant_row5, quant_row6, quant_row7,
workspace_l + 4 * DCTSIZE / 2,
workspace_r + 4 * DCTSIZE / 2);
}
}
/* Second pass: compute IDCT on rows in workspace. */
/* If all coefficients in right 4x8 block are 0, use "sparse" second pass. */
if (right_ac_dc_bitmap == 0) {
jsimd_idct_islow_pass2_sparse(workspace_l, output_buf, output_col, 0);
jsimd_idct_islow_pass2_sparse(workspace_r, output_buf, output_col, 4);
} else {
jsimd_idct_islow_pass2_regular(workspace_l, output_buf, output_col, 0);
jsimd_idct_islow_pass2_regular(workspace_r, output_buf, output_col, 4);
}
}
/* Perform dequantization and the first pass of the accurate inverse DCT on a
* 4x8 block of coefficients. (To process the full 8x8 DCT block, this
* function-- or some other optimized variant-- needs to be called for both the
* left and right 4x8 blocks.)
*
* This "regular" version assumes that no optimization can be made to the IDCT
* calculation, since no useful set of AC coefficients is all 0.
*
* The original C implementation of the accurate IDCT (jpeg_idct_slow()) can be
* found in jidctint.c. Algorithmic changes made here are documented inline.
*/
static INLINE void jsimd_idct_islow_pass1_regular(int16x4_t row0,
int16x4_t row1,
int16x4_t row2,
int16x4_t row3,
int16x4_t row4,
int16x4_t row5,
int16x4_t row6,
int16x4_t row7,
int16x4_t quant_row0,
int16x4_t quant_row1,
int16x4_t quant_row2,
int16x4_t quant_row3,
int16x4_t quant_row4,
int16x4_t quant_row5,
int16x4_t quant_row6,
int16x4_t quant_row7,
int16_t *workspace_1,
int16_t *workspace_2)
{
/* Load constants for IDCT computation. */
#ifdef HAVE_VLD1_S16_X3
const int16x4x3_t consts = vld1_s16_x3(jsimd_idct_islow_neon_consts);
#else
const int16x4_t consts1 = vld1_s16(jsimd_idct_islow_neon_consts);
const int16x4_t consts2 = vld1_s16(jsimd_idct_islow_neon_consts + 4);
const int16x4_t consts3 = vld1_s16(jsimd_idct_islow_neon_consts + 8);
const int16x4x3_t consts = { { consts1, consts2, consts3 } };
#endif
/* Even part */
int16x4_t z2_s16 = vmul_s16(row2, quant_row2);
int16x4_t z3_s16 = vmul_s16(row6, quant_row6);
int32x4_t tmp2 = vmull_lane_s16(z2_s16, consts.val[0], 1);
int32x4_t tmp3 = vmull_lane_s16(z2_s16, consts.val[1], 2);
tmp2 = vmlal_lane_s16(tmp2, z3_s16, consts.val[2], 1);
tmp3 = vmlal_lane_s16(tmp3, z3_s16, consts.val[0], 1);
z2_s16 = vmul_s16(row0, quant_row0);
z3_s16 = vmul_s16(row4, quant_row4);
int32x4_t tmp0 = vshll_n_s16(vadd_s16(z2_s16, z3_s16), CONST_BITS);
int32x4_t tmp1 = vshll_n_s16(vsub_s16(z2_s16, z3_s16), CONST_BITS);
int32x4_t tmp10 = vaddq_s32(tmp0, tmp3);
int32x4_t tmp13 = vsubq_s32(tmp0, tmp3);
int32x4_t tmp11 = vaddq_s32(tmp1, tmp2);
int32x4_t tmp12 = vsubq_s32(tmp1, tmp2);
/* Odd part */
int16x4_t tmp0_s16 = vmul_s16(row7, quant_row7);
int16x4_t tmp1_s16 = vmul_s16(row5, quant_row5);
int16x4_t tmp2_s16 = vmul_s16(row3, quant_row3);
int16x4_t tmp3_s16 = vmul_s16(row1, quant_row1);
z3_s16 = vadd_s16(tmp0_s16, tmp2_s16);
int16x4_t z4_s16 = vadd_s16(tmp1_s16, tmp3_s16);
/* Implementation as per jpeg_idct_islow() in jidctint.c:
* z5 = (z3 + z4) * 1.175875602;
* z3 = z3 * -1.961570560; z4 = z4 * -0.390180644;
* z3 += z5; z4 += z5;
*
* This implementation:
* z3 = z3 * (1.175875602 - 1.961570560) + z4 * 1.175875602;
* z4 = z3 * 1.175875602 + z4 * (1.175875602 - 0.390180644);
*/
int32x4_t z3 = vmull_lane_s16(z3_s16, consts.val[2], 3);
int32x4_t z4 = vmull_lane_s16(z3_s16, consts.val[1], 3);
z3 = vmlal_lane_s16(z3, z4_s16, consts.val[1], 3);
z4 = vmlal_lane_s16(z4, z4_s16, consts.val[2], 0);
/* Implementation as per jpeg_idct_islow() in jidctint.c:
* z1 = tmp0 + tmp3; z2 = tmp1 + tmp2;
* tmp0 = tmp0 * 0.298631336; tmp1 = tmp1 * 2.053119869;
* tmp2 = tmp2 * 3.072711026; tmp3 = tmp3 * 1.501321110;
* z1 = z1 * -0.899976223; z2 = z2 * -2.562915447;
* tmp0 += z1 + z3; tmp1 += z2 + z4;
* tmp2 += z2 + z3; tmp3 += z1 + z4;
*
* This implementation:
* tmp0 = tmp0 * (0.298631336 - 0.899976223) + tmp3 * -0.899976223;
* tmp1 = tmp1 * (2.053119869 - 2.562915447) + tmp2 * -2.562915447;
* tmp2 = tmp1 * -2.562915447 + tmp2 * (3.072711026 - 2.562915447);
* tmp3 = tmp0 * -0.899976223 + tmp3 * (1.501321110 - 0.899976223);
* tmp0 += z3; tmp1 += z4;
* tmp2 += z3; tmp3 += z4;
*/
tmp0 = vmull_lane_s16(tmp0_s16, consts.val[0], 3);
tmp1 = vmull_lane_s16(tmp1_s16, consts.val[1], 1);
tmp2 = vmull_lane_s16(tmp2_s16, consts.val[2], 2);
tmp3 = vmull_lane_s16(tmp3_s16, consts.val[1], 0);
tmp0 = vmlsl_lane_s16(tmp0, tmp3_s16, consts.val[0], 0);
tmp1 = vmlsl_lane_s16(tmp1, tmp2_s16, consts.val[0], 2);
tmp2 = vmlsl_lane_s16(tmp2, tmp1_s16, consts.val[0], 2);
tmp3 = vmlsl_lane_s16(tmp3, tmp0_s16, consts.val[0], 0);
tmp0 = vaddq_s32(tmp0, z3);
tmp1 = vaddq_s32(tmp1, z4);
tmp2 = vaddq_s32(tmp2, z3);
tmp3 = vaddq_s32(tmp3, z4);
/* Final output stage: descale and narrow to 16-bit. */
int16x4x4_t rows_0123 = { {
vrshrn_n_s32(vaddq_s32(tmp10, tmp3), DESCALE_P1),
vrshrn_n_s32(vaddq_s32(tmp11, tmp2), DESCALE_P1),
vrshrn_n_s32(vaddq_s32(tmp12, tmp1), DESCALE_P1),
vrshrn_n_s32(vaddq_s32(tmp13, tmp0), DESCALE_P1)
} };
int16x4x4_t rows_4567 = { {
vrshrn_n_s32(vsubq_s32(tmp13, tmp0), DESCALE_P1),
vrshrn_n_s32(vsubq_s32(tmp12, tmp1), DESCALE_P1),
vrshrn_n_s32(vsubq_s32(tmp11, tmp2), DESCALE_P1),
vrshrn_n_s32(vsubq_s32(tmp10, tmp3), DESCALE_P1)
} };
/* Store 4x4 blocks to the intermediate workspace, ready for the second pass.
* (VST4 transposes the blocks. We need to operate on rows in the next
* pass.)
*/
vst4_s16(workspace_1, rows_0123);
vst4_s16(workspace_2, rows_4567);
}
/* Perform dequantization and the first pass of the accurate inverse DCT on a
* 4x8 block of coefficients.
*
* This "sparse" version assumes that the AC coefficients in rows 4-7 are all
* 0. This simplifies the IDCT calculation, accelerating overall performance.
*/
static INLINE void jsimd_idct_islow_pass1_sparse(int16x4_t row0,
int16x4_t row1,
int16x4_t row2,
int16x4_t row3,
int16x4_t quant_row0,
int16x4_t quant_row1,
int16x4_t quant_row2,
int16x4_t quant_row3,
int16_t *workspace_1,
int16_t *workspace_2)
{
/* Load constants for IDCT computation. */
#ifdef HAVE_VLD1_S16_X3
const int16x4x3_t consts = vld1_s16_x3(jsimd_idct_islow_neon_consts);
#else
const int16x4_t consts1 = vld1_s16(jsimd_idct_islow_neon_consts);
const int16x4_t consts2 = vld1_s16(jsimd_idct_islow_neon_consts + 4);
const int16x4_t consts3 = vld1_s16(jsimd_idct_islow_neon_consts + 8);
const int16x4x3_t consts = { { consts1, consts2, consts3 } };
#endif
/* Even part (z3 is all 0) */
int16x4_t z2_s16 = vmul_s16(row2, quant_row2);
int32x4_t tmp2 = vmull_lane_s16(z2_s16, consts.val[0], 1);
int32x4_t tmp3 = vmull_lane_s16(z2_s16, consts.val[1], 2);
z2_s16 = vmul_s16(row0, quant_row0);
int32x4_t tmp0 = vshll_n_s16(z2_s16, CONST_BITS);
int32x4_t tmp1 = vshll_n_s16(z2_s16, CONST_BITS);
int32x4_t tmp10 = vaddq_s32(tmp0, tmp3);
int32x4_t tmp13 = vsubq_s32(tmp0, tmp3);
int32x4_t tmp11 = vaddq_s32(tmp1, tmp2);
int32x4_t tmp12 = vsubq_s32(tmp1, tmp2);
/* Odd part (tmp0 and tmp1 are both all 0) */
int16x4_t tmp2_s16 = vmul_s16(row3, quant_row3);
int16x4_t tmp3_s16 = vmul_s16(row1, quant_row1);
int16x4_t z3_s16 = tmp2_s16;
int16x4_t z4_s16 = tmp3_s16;
int32x4_t z3 = vmull_lane_s16(z3_s16, consts.val[2], 3);
int32x4_t z4 = vmull_lane_s16(z3_s16, consts.val[1], 3);
z3 = vmlal_lane_s16(z3, z4_s16, consts.val[1], 3);
z4 = vmlal_lane_s16(z4, z4_s16, consts.val[2], 0);
tmp0 = vmlsl_lane_s16(z3, tmp3_s16, consts.val[0], 0);
tmp1 = vmlsl_lane_s16(z4, tmp2_s16, consts.val[0], 2);
tmp2 = vmlal_lane_s16(z3, tmp2_s16, consts.val[2], 2);
tmp3 = vmlal_lane_s16(z4, tmp3_s16, consts.val[1], 0);
/* Final output stage: descale and narrow to 16-bit. */
int16x4x4_t rows_0123 = { {
vrshrn_n_s32(vaddq_s32(tmp10, tmp3), DESCALE_P1),
vrshrn_n_s32(vaddq_s32(tmp11, tmp2), DESCALE_P1),
vrshrn_n_s32(vaddq_s32(tmp12, tmp1), DESCALE_P1),
vrshrn_n_s32(vaddq_s32(tmp13, tmp0), DESCALE_P1)
} };
int16x4x4_t rows_4567 = { {
vrshrn_n_s32(vsubq_s32(tmp13, tmp0), DESCALE_P1),
vrshrn_n_s32(vsubq_s32(tmp12, tmp1), DESCALE_P1),
vrshrn_n_s32(vsubq_s32(tmp11, tmp2), DESCALE_P1),
vrshrn_n_s32(vsubq_s32(tmp10, tmp3), DESCALE_P1)
} };
/* Store 4x4 blocks to the intermediate workspace, ready for the second pass.
* (VST4 transposes the blocks. We need to operate on rows in the next
* pass.)
*/
vst4_s16(workspace_1, rows_0123);
vst4_s16(workspace_2, rows_4567);
}
/* Perform the second pass of the accurate inverse DCT on a 4x8 block of
* coefficients. (To process the full 8x8 DCT block, this function-- or some
* other optimized variant-- needs to be called for both the right and left 4x8
* blocks.)
*
* This "regular" version assumes that no optimization can be made to the IDCT
* calculation, since no useful set of coefficient values are all 0 after the
* first pass.
*
* Again, the original C implementation of the accurate IDCT (jpeg_idct_slow())
* can be found in jidctint.c. Algorithmic changes made here are documented
* inline.
*/
static INLINE void jsimd_idct_islow_pass2_regular(int16_t *workspace,
JSAMPARRAY output_buf,
JDIMENSION output_col,
unsigned buf_offset)
{
/* Load constants for IDCT computation. */
#ifdef HAVE_VLD1_S16_X3
const int16x4x3_t consts = vld1_s16_x3(jsimd_idct_islow_neon_consts);
#else
const int16x4_t consts1 = vld1_s16(jsimd_idct_islow_neon_consts);
const int16x4_t consts2 = vld1_s16(jsimd_idct_islow_neon_consts + 4);
const int16x4_t consts3 = vld1_s16(jsimd_idct_islow_neon_consts + 8);
const int16x4x3_t consts = { { consts1, consts2, consts3 } };
#endif
/* Even part */
int16x4_t z2_s16 = vld1_s16(workspace + 2 * DCTSIZE / 2);
int16x4_t z3_s16 = vld1_s16(workspace + 6 * DCTSIZE / 2);
int32x4_t tmp2 = vmull_lane_s16(z2_s16, consts.val[0], 1);
int32x4_t tmp3 = vmull_lane_s16(z2_s16, consts.val[1], 2);
tmp2 = vmlal_lane_s16(tmp2, z3_s16, consts.val[2], 1);
tmp3 = vmlal_lane_s16(tmp3, z3_s16, consts.val[0], 1);
z2_s16 = vld1_s16(workspace + 0 * DCTSIZE / 2);
z3_s16 = vld1_s16(workspace + 4 * DCTSIZE / 2);
int32x4_t tmp0 = vshll_n_s16(vadd_s16(z2_s16, z3_s16), CONST_BITS);
int32x4_t tmp1 = vshll_n_s16(vsub_s16(z2_s16, z3_s16), CONST_BITS);
int32x4_t tmp10 = vaddq_s32(tmp0, tmp3);
int32x4_t tmp13 = vsubq_s32(tmp0, tmp3);
int32x4_t tmp11 = vaddq_s32(tmp1, tmp2);
int32x4_t tmp12 = vsubq_s32(tmp1, tmp2);
/* Odd part */
int16x4_t tmp0_s16 = vld1_s16(workspace + 7 * DCTSIZE / 2);
int16x4_t tmp1_s16 = vld1_s16(workspace + 5 * DCTSIZE / 2);
int16x4_t tmp2_s16 = vld1_s16(workspace + 3 * DCTSIZE / 2);
int16x4_t tmp3_s16 = vld1_s16(workspace + 1 * DCTSIZE / 2);
z3_s16 = vadd_s16(tmp0_s16, tmp2_s16);
int16x4_t z4_s16 = vadd_s16(tmp1_s16, tmp3_s16);
/* Implementation as per jpeg_idct_islow() in jidctint.c:
* z5 = (z3 + z4) * 1.175875602;
* z3 = z3 * -1.961570560; z4 = z4 * -0.390180644;
* z3 += z5; z4 += z5;
*
* This implementation:
* z3 = z3 * (1.175875602 - 1.961570560) + z4 * 1.175875602;
* z4 = z3 * 1.175875602 + z4 * (1.175875602 - 0.390180644);
*/
int32x4_t z3 = vmull_lane_s16(z3_s16, consts.val[2], 3);
int32x4_t z4 = vmull_lane_s16(z3_s16, consts.val[1], 3);
z3 = vmlal_lane_s16(z3, z4_s16, consts.val[1], 3);
z4 = vmlal_lane_s16(z4, z4_s16, consts.val[2], 0);
/* Implementation as per jpeg_idct_islow() in jidctint.c:
* z1 = tmp0 + tmp3; z2 = tmp1 + tmp2;
* tmp0 = tmp0 * 0.298631336; tmp1 = tmp1 * 2.053119869;
* tmp2 = tmp2 * 3.072711026; tmp3 = tmp3 * 1.501321110;
* z1 = z1 * -0.899976223; z2 = z2 * -2.562915447;
* tmp0 += z1 + z3; tmp1 += z2 + z4;
* tmp2 += z2 + z3; tmp3 += z1 + z4;
*
* This implementation:
* tmp0 = tmp0 * (0.298631336 - 0.899976223) + tmp3 * -0.899976223;
* tmp1 = tmp1 * (2.053119869 - 2.562915447) + tmp2 * -2.562915447;
* tmp2 = tmp1 * -2.562915447 + tmp2 * (3.072711026 - 2.562915447);
* tmp3 = tmp0 * -0.899976223 + tmp3 * (1.501321110 - 0.899976223);
* tmp0 += z3; tmp1 += z4;
* tmp2 += z3; tmp3 += z4;
*/
tmp0 = vmull_lane_s16(tmp0_s16, consts.val[0], 3);
tmp1 = vmull_lane_s16(tmp1_s16, consts.val[1], 1);
tmp2 = vmull_lane_s16(tmp2_s16, consts.val[2], 2);
tmp3 = vmull_lane_s16(tmp3_s16, consts.val[1], 0);
tmp0 = vmlsl_lane_s16(tmp0, tmp3_s16, consts.val[0], 0);
tmp1 = vmlsl_lane_s16(tmp1, tmp2_s16, consts.val[0], 2);
tmp2 = vmlsl_lane_s16(tmp2, tmp1_s16, consts.val[0], 2);
tmp3 = vmlsl_lane_s16(tmp3, tmp0_s16, consts.val[0], 0);
tmp0 = vaddq_s32(tmp0, z3);
tmp1 = vaddq_s32(tmp1, z4);
tmp2 = vaddq_s32(tmp2, z3);
tmp3 = vaddq_s32(tmp3, z4);
/* Final output stage: descale and narrow to 16-bit. */
int16x8_t cols_02_s16 = vcombine_s16(vaddhn_s32(tmp10, tmp3),
vaddhn_s32(tmp12, tmp1));
int16x8_t cols_13_s16 = vcombine_s16(vaddhn_s32(tmp11, tmp2),
vaddhn_s32(tmp13, tmp0));
int16x8_t cols_46_s16 = vcombine_s16(vsubhn_s32(tmp13, tmp0),
vsubhn_s32(tmp11, tmp2));
int16x8_t cols_57_s16 = vcombine_s16(vsubhn_s32(tmp12, tmp1),
vsubhn_s32(tmp10, tmp3));
/* Descale and narrow to 8-bit. */
int8x8_t cols_02_s8 = vqrshrn_n_s16(cols_02_s16, DESCALE_P2 - 16);
int8x8_t cols_13_s8 = vqrshrn_n_s16(cols_13_s16, DESCALE_P2 - 16);
int8x8_t cols_46_s8 = vqrshrn_n_s16(cols_46_s16, DESCALE_P2 - 16);
int8x8_t cols_57_s8 = vqrshrn_n_s16(cols_57_s16, DESCALE_P2 - 16);
/* Clamp to range [0-255]. */
uint8x8_t cols_02_u8 = vadd_u8(vreinterpret_u8_s8(cols_02_s8),
vdup_n_u8(CENTERJSAMPLE));
uint8x8_t cols_13_u8 = vadd_u8(vreinterpret_u8_s8(cols_13_s8),
vdup_n_u8(CENTERJSAMPLE));
uint8x8_t cols_46_u8 = vadd_u8(vreinterpret_u8_s8(cols_46_s8),
vdup_n_u8(CENTERJSAMPLE));
uint8x8_t cols_57_u8 = vadd_u8(vreinterpret_u8_s8(cols_57_s8),
vdup_n_u8(CENTERJSAMPLE));
/* Transpose 4x8 block and store to memory. (Zipping adjacent columns
* together allows us to store 16-bit elements.)
*/
uint8x8x2_t cols_01_23 = vzip_u8(cols_02_u8, cols_13_u8);
uint8x8x2_t cols_45_67 = vzip_u8(cols_46_u8, cols_57_u8);
uint16x4x4_t cols_01_23_45_67 = { {
vreinterpret_u16_u8(cols_01_23.val[0]),
vreinterpret_u16_u8(cols_01_23.val[1]),
vreinterpret_u16_u8(cols_45_67.val[0]),
vreinterpret_u16_u8(cols_45_67.val[1])
} };
JSAMPROW outptr0 = output_buf[buf_offset + 0] + output_col;
JSAMPROW outptr1 = output_buf[buf_offset + 1] + output_col;
JSAMPROW outptr2 = output_buf[buf_offset + 2] + output_col;
JSAMPROW outptr3 = output_buf[buf_offset + 3] + output_col;
/* VST4 of 16-bit elements completes the transpose. */
vst4_lane_u16((uint16_t *)outptr0, cols_01_23_45_67, 0);
vst4_lane_u16((uint16_t *)outptr1, cols_01_23_45_67, 1);
vst4_lane_u16((uint16_t *)outptr2, cols_01_23_45_67, 2);
vst4_lane_u16((uint16_t *)outptr3, cols_01_23_45_67, 3);
}
/* Performs the second pass of the accurate inverse DCT on a 4x8 block
* of coefficients.
*
* This "sparse" version assumes that the coefficient values (after the first
* pass) in rows 4-7 are all 0. This simplifies the IDCT calculation,
* accelerating overall performance.
*/
static INLINE void jsimd_idct_islow_pass2_sparse(int16_t *workspace,
JSAMPARRAY output_buf,
JDIMENSION output_col,
unsigned buf_offset)
{
/* Load constants for IDCT computation. */
#ifdef HAVE_VLD1_S16_X3
const int16x4x3_t consts = vld1_s16_x3(jsimd_idct_islow_neon_consts);
#else
const int16x4_t consts1 = vld1_s16(jsimd_idct_islow_neon_consts);
const int16x4_t consts2 = vld1_s16(jsimd_idct_islow_neon_consts + 4);
const int16x4_t consts3 = vld1_s16(jsimd_idct_islow_neon_consts + 8);
const int16x4x3_t consts = { { consts1, consts2, consts3 } };
#endif
/* Even part (z3 is all 0) */
int16x4_t z2_s16 = vld1_s16(workspace + 2 * DCTSIZE / 2);
int32x4_t tmp2 = vmull_lane_s16(z2_s16, consts.val[0], 1);
int32x4_t tmp3 = vmull_lane_s16(z2_s16, consts.val[1], 2);
z2_s16 = vld1_s16(workspace + 0 * DCTSIZE / 2);
int32x4_t tmp0 = vshll_n_s16(z2_s16, CONST_BITS);
int32x4_t tmp1 = vshll_n_s16(z2_s16, CONST_BITS);
int32x4_t tmp10 = vaddq_s32(tmp0, tmp3);
int32x4_t tmp13 = vsubq_s32(tmp0, tmp3);
int32x4_t tmp11 = vaddq_s32(tmp1, tmp2);
int32x4_t tmp12 = vsubq_s32(tmp1, tmp2);
/* Odd part (tmp0 and tmp1 are both all 0) */
int16x4_t tmp2_s16 = vld1_s16(workspace + 3 * DCTSIZE / 2);
int16x4_t tmp3_s16 = vld1_s16(workspace + 1 * DCTSIZE / 2);
int16x4_t z3_s16 = tmp2_s16;
int16x4_t z4_s16 = tmp3_s16;
int32x4_t z3 = vmull_lane_s16(z3_s16, consts.val[2], 3);
z3 = vmlal_lane_s16(z3, z4_s16, consts.val[1], 3);
int32x4_t z4 = vmull_lane_s16(z3_s16, consts.val[1], 3);
z4 = vmlal_lane_s16(z4, z4_s16, consts.val[2], 0);
tmp0 = vmlsl_lane_s16(z3, tmp3_s16, consts.val[0], 0);
tmp1 = vmlsl_lane_s16(z4, tmp2_s16, consts.val[0], 2);
tmp2 = vmlal_lane_s16(z3, tmp2_s16, consts.val[2], 2);
tmp3 = vmlal_lane_s16(z4, tmp3_s16, consts.val[1], 0);
/* Final output stage: descale and narrow to 16-bit. */
int16x8_t cols_02_s16 = vcombine_s16(vaddhn_s32(tmp10, tmp3),
vaddhn_s32(tmp12, tmp1));
int16x8_t cols_13_s16 = vcombine_s16(vaddhn_s32(tmp11, tmp2),
vaddhn_s32(tmp13, tmp0));
int16x8_t cols_46_s16 = vcombine_s16(vsubhn_s32(tmp13, tmp0),
vsubhn_s32(tmp11, tmp2));
int16x8_t cols_57_s16 = vcombine_s16(vsubhn_s32(tmp12, tmp1),
vsubhn_s32(tmp10, tmp3));
/* Descale and narrow to 8-bit. */
int8x8_t cols_02_s8 = vqrshrn_n_s16(cols_02_s16, DESCALE_P2 - 16);
int8x8_t cols_13_s8 = vqrshrn_n_s16(cols_13_s16, DESCALE_P2 - 16);
int8x8_t cols_46_s8 = vqrshrn_n_s16(cols_46_s16, DESCALE_P2 - 16);
int8x8_t cols_57_s8 = vqrshrn_n_s16(cols_57_s16, DESCALE_P2 - 16);
/* Clamp to range [0-255]. */
uint8x8_t cols_02_u8 = vadd_u8(vreinterpret_u8_s8(cols_02_s8),
vdup_n_u8(CENTERJSAMPLE));
uint8x8_t cols_13_u8 = vadd_u8(vreinterpret_u8_s8(cols_13_s8),
vdup_n_u8(CENTERJSAMPLE));
uint8x8_t cols_46_u8 = vadd_u8(vreinterpret_u8_s8(cols_46_s8),
vdup_n_u8(CENTERJSAMPLE));
uint8x8_t cols_57_u8 = vadd_u8(vreinterpret_u8_s8(cols_57_s8),
vdup_n_u8(CENTERJSAMPLE));
/* Transpose 4x8 block and store to memory. (Zipping adjacent columns
* together allows us to store 16-bit elements.)
*/
uint8x8x2_t cols_01_23 = vzip_u8(cols_02_u8, cols_13_u8);
uint8x8x2_t cols_45_67 = vzip_u8(cols_46_u8, cols_57_u8);
uint16x4x4_t cols_01_23_45_67 = { {
vreinterpret_u16_u8(cols_01_23.val[0]),
vreinterpret_u16_u8(cols_01_23.val[1]),
vreinterpret_u16_u8(cols_45_67.val[0]),
vreinterpret_u16_u8(cols_45_67.val[1])
} };
JSAMPROW outptr0 = output_buf[buf_offset + 0] + output_col;
JSAMPROW outptr1 = output_buf[buf_offset + 1] + output_col;
JSAMPROW outptr2 = output_buf[buf_offset + 2] + output_col;
JSAMPROW outptr3 = output_buf[buf_offset + 3] + output_col;
/* VST4 of 16-bit elements completes the transpose. */
vst4_lane_u16((uint16_t *)outptr0, cols_01_23_45_67, 0);
vst4_lane_u16((uint16_t *)outptr1, cols_01_23_45_67, 1);
vst4_lane_u16((uint16_t *)outptr2, cols_01_23_45_67, 2);
vst4_lane_u16((uint16_t *)outptr3, cols_01_23_45_67, 3);
}