Source code
Revision control
Copy as Markdown
Other Tools
/*
* Loongson MMI optimizations for libjpeg-turbo
*
* Copyright (C) 2014, 2018, 2020, D. R. Commander. All Rights Reserved.
* Copyright (C) 2016-2017, Loongson Technology Corporation Limited, BeiJing.
* All Rights Reserved.
* Authors: ZhuChen <zhuchen@loongson.cn>
* CaiWanwei <caiwanwei@loongson.cn>
* SunZhangzhi <sunzhangzhi-cq@loongson.cn>
*
* Based on the x86 SIMD extension for IJG JPEG library
* Copyright (C) 1999-2006, MIYASAKA Masaru.
*
* 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.
*/
/* ACCURATE INTEGER FORWARD DCT */
#include "jsimd_mmi.h"
#define CONST_BITS 13
#define PASS1_BITS 2
#define DESCALE_P1 (CONST_BITS - PASS1_BITS)
#define DESCALE_P2 (CONST_BITS + PASS1_BITS)
#define FIX_0_298 ((short)2446) /* FIX(0.298631336) */
#define FIX_0_390 ((short)3196) /* FIX(0.390180644) */
#define FIX_0_541 ((short)4433) /* FIX(0.541196100) */
#define FIX_0_765 ((short)6270) /* FIX(0.765366865) */
#define FIX_0_899 ((short)7373) /* FIX(0.899976223) */
#define FIX_1_175 ((short)9633) /* FIX(1.175875602) */
#define FIX_1_501 ((short)12299) /* FIX(1.501321110) */
#define FIX_1_847 ((short)15137) /* FIX(1.847759065) */
#define FIX_1_961 ((short)16069) /* FIX(1.961570560) */
#define FIX_2_053 ((short)16819) /* FIX(2.053119869) */
#define FIX_2_562 ((short)20995) /* FIX(2.562915447) */
#define FIX_3_072 ((short)25172) /* FIX(3.072711026) */
enum const_index {
index_PW_F130_F054,
index_PW_F054_MF130,
index_PW_MF078_F117,
index_PW_F117_F078,
index_PW_MF060_MF089,
index_PW_MF089_F060,
index_PW_MF050_MF256,
index_PW_MF256_F050,
index_PD_DESCALE_P1,
index_PD_DESCALE_P2,
index_PW_DESCALE_P2X
};
static uint64_t const_value[] = {
_uint64_set_pi16(FIX_0_541, (FIX_0_541 + FIX_0_765),
FIX_0_541, (FIX_0_541 + FIX_0_765)),
_uint64_set_pi16((FIX_0_541 - FIX_1_847), FIX_0_541,
(FIX_0_541 - FIX_1_847), FIX_0_541),
_uint64_set_pi16(FIX_1_175, (FIX_1_175 - FIX_1_961),
FIX_1_175, (FIX_1_175 - FIX_1_961)),
_uint64_set_pi16((FIX_1_175 - FIX_0_390), FIX_1_175,
(FIX_1_175 - FIX_0_390), FIX_1_175),
_uint64_set_pi16(-FIX_0_899, (FIX_0_298 - FIX_0_899),
-FIX_0_899, (FIX_0_298 - FIX_0_899)),
_uint64_set_pi16((FIX_1_501 - FIX_0_899), -FIX_0_899,
(FIX_1_501 - FIX_0_899), -FIX_0_899),
_uint64_set_pi16(-FIX_2_562, (FIX_2_053 - FIX_2_562),
-FIX_2_562, (FIX_2_053 - FIX_2_562)),
_uint64_set_pi16((FIX_3_072 - FIX_2_562), -FIX_2_562,
(FIX_3_072 - FIX_2_562), -FIX_2_562),
_uint64_set_pi32((1 << (DESCALE_P1 - 1)), (1 << (DESCALE_P1 - 1))),
_uint64_set_pi32((1 << (DESCALE_P2 - 1)), (1 << (DESCALE_P2 - 1))),
_uint64_set_pi16((1 << (PASS1_BITS - 1)), (1 << (PASS1_BITS - 1)),
(1 << (PASS1_BITS - 1)), (1 << (PASS1_BITS - 1)))
};
#define PW_F130_F054 get_const_value(index_PW_F130_F054)
#define PW_F054_MF130 get_const_value(index_PW_F054_MF130)
#define PW_MF078_F117 get_const_value(index_PW_MF078_F117)
#define PW_F117_F078 get_const_value(index_PW_F117_F078)
#define PW_MF060_MF089 get_const_value(index_PW_MF060_MF089)
#define PW_MF089_F060 get_const_value(index_PW_MF089_F060)
#define PW_MF050_MF256 get_const_value(index_PW_MF050_MF256)
#define PW_MF256_F050 get_const_value(index_PW_MF256_F050)
#define PD_DESCALE_P1 get_const_value(index_PD_DESCALE_P1)
#define PD_DESCALE_P2 get_const_value(index_PD_DESCALE_P2)
#define PW_DESCALE_P2X get_const_value(index_PW_DESCALE_P2X)
#define DO_FDCT_COMMON(PASS) { \
__m64 tmp1312l, tmp1312h, tmp47l, tmp47h, tmp4l, tmp4h, tmp7l, tmp7h; \
__m64 tmp56l, tmp56h, tmp5l, tmp5h, tmp6l, tmp6h; \
__m64 out1l, out1h, out2l, out2h, out3l, out3h; \
__m64 out5l, out5h, out6l, out6h, out7l, out7h; \
__m64 z34l, z34h, z3l, z3h, z4l, z4h, z3, z4; \
\
/* (Original) \
* z1 = (tmp12 + tmp13) * 0.541196100; \
* out2 = z1 + tmp13 * 0.765366865; \
* out6 = z1 + tmp12 * -1.847759065; \
* \
* (This implementation) \
* out2 = tmp13 * (0.541196100 + 0.765366865) + tmp12 * 0.541196100; \
* out6 = tmp13 * 0.541196100 + tmp12 * (0.541196100 - 1.847759065); \
*/ \
\
tmp1312l = _mm_unpacklo_pi16(tmp13, tmp12); \
tmp1312h = _mm_unpackhi_pi16(tmp13, tmp12); \
\
out2l = _mm_madd_pi16(tmp1312l, PW_F130_F054); \
out2h = _mm_madd_pi16(tmp1312h, PW_F130_F054); \
out6l = _mm_madd_pi16(tmp1312l, PW_F054_MF130); \
out6h = _mm_madd_pi16(tmp1312h, PW_F054_MF130); \
\
out2l = _mm_add_pi32(out2l, PD_DESCALE_P##PASS); \
out2h = _mm_add_pi32(out2h, PD_DESCALE_P##PASS); \
out2l = _mm_srai_pi32(out2l, DESCALE_P##PASS); \
out2h = _mm_srai_pi32(out2h, DESCALE_P##PASS); \
\
out6l = _mm_add_pi32(out6l, PD_DESCALE_P##PASS); \
out6h = _mm_add_pi32(out6h, PD_DESCALE_P##PASS); \
out6l = _mm_srai_pi32(out6l, DESCALE_P##PASS); \
out6h = _mm_srai_pi32(out6h, DESCALE_P##PASS); \
\
out2 = _mm_packs_pi32(out2l, out2h); \
out6 = _mm_packs_pi32(out6l, out6h); \
\
/* Odd part */ \
\
z3 = _mm_add_pi16(tmp4, tmp6); \
z4 = _mm_add_pi16(tmp5, tmp7); \
\
/* (Original) \
* 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); \
*/ \
\
z34l = _mm_unpacklo_pi16(z3, z4); \
z34h = _mm_unpackhi_pi16(z3, z4); \
z3l = _mm_madd_pi16(z34l, PW_MF078_F117); \
z3h = _mm_madd_pi16(z34h, PW_MF078_F117); \
z4l = _mm_madd_pi16(z34l, PW_F117_F078); \
z4h = _mm_madd_pi16(z34h, PW_F117_F078); \
\
/* (Original) \
* z1 = tmp4 + tmp7; z2 = tmp5 + tmp6; \
* tmp4 = tmp4 * 0.298631336; tmp5 = tmp5 * 2.053119869; \
* tmp6 = tmp6 * 3.072711026; tmp7 = tmp7 * 1.501321110; \
* z1 = z1 * -0.899976223; z2 = z2 * -2.562915447; \
* out7 = tmp4 + z1 + z3; out5 = tmp5 + z2 + z4; \
* out3 = tmp6 + z2 + z3; out1 = tmp7 + z1 + z4; \
* \
* (This implementation) \
* tmp4 = tmp4 * (0.298631336 - 0.899976223) + tmp7 * -0.899976223; \
* tmp5 = tmp5 * (2.053119869 - 2.562915447) + tmp6 * -2.562915447; \
* tmp6 = tmp5 * -2.562915447 + tmp6 * (3.072711026 - 2.562915447); \
* tmp7 = tmp4 * -0.899976223 + tmp7 * (1.501321110 - 0.899976223); \
* out7 = tmp4 + z3; out5 = tmp5 + z4; \
* out3 = tmp6 + z3; out1 = tmp7 + z4; \
*/ \
\
tmp47l = _mm_unpacklo_pi16(tmp4, tmp7); \
tmp47h = _mm_unpackhi_pi16(tmp4, tmp7); \
\
tmp4l = _mm_madd_pi16(tmp47l, PW_MF060_MF089); \
tmp4h = _mm_madd_pi16(tmp47h, PW_MF060_MF089); \
tmp7l = _mm_madd_pi16(tmp47l, PW_MF089_F060); \
tmp7h = _mm_madd_pi16(tmp47h, PW_MF089_F060); \
\
out7l = _mm_add_pi32(tmp4l, z3l); \
out7h = _mm_add_pi32(tmp4h, z3h); \
out1l = _mm_add_pi32(tmp7l, z4l); \
out1h = _mm_add_pi32(tmp7h, z4h); \
\
out7l = _mm_add_pi32(out7l, PD_DESCALE_P##PASS); \
out7h = _mm_add_pi32(out7h, PD_DESCALE_P##PASS); \
out7l = _mm_srai_pi32(out7l, DESCALE_P##PASS); \
out7h = _mm_srai_pi32(out7h, DESCALE_P##PASS); \
\
out1l = _mm_add_pi32(out1l, PD_DESCALE_P##PASS); \
out1h = _mm_add_pi32(out1h, PD_DESCALE_P##PASS); \
out1l = _mm_srai_pi32(out1l, DESCALE_P##PASS); \
out1h = _mm_srai_pi32(out1h, DESCALE_P##PASS); \
\
out7 = _mm_packs_pi32(out7l, out7h); \
out1 = _mm_packs_pi32(out1l, out1h); \
\
tmp56l = _mm_unpacklo_pi16(tmp5, tmp6); \
tmp56h = _mm_unpackhi_pi16(tmp5, tmp6); \
\
tmp5l = _mm_madd_pi16(tmp56l, PW_MF050_MF256); \
tmp5h = _mm_madd_pi16(tmp56h, PW_MF050_MF256); \
tmp6l = _mm_madd_pi16(tmp56l, PW_MF256_F050); \
tmp6h = _mm_madd_pi16(tmp56h, PW_MF256_F050); \
\
out5l = _mm_add_pi32(tmp5l, z4l); \
out5h = _mm_add_pi32(tmp5h, z4h); \
out3l = _mm_add_pi32(tmp6l, z3l); \
out3h = _mm_add_pi32(tmp6h, z3h); \
\
out5l = _mm_add_pi32(out5l, PD_DESCALE_P##PASS); \
out5h = _mm_add_pi32(out5h, PD_DESCALE_P##PASS); \
out5l = _mm_srai_pi32(out5l, DESCALE_P##PASS); \
out5h = _mm_srai_pi32(out5h, DESCALE_P##PASS); \
\
out3l = _mm_add_pi32(out3l, PD_DESCALE_P##PASS); \
out3h = _mm_add_pi32(out3h, PD_DESCALE_P##PASS); \
out3l = _mm_srai_pi32(out3l, DESCALE_P##PASS); \
out3h = _mm_srai_pi32(out3h, DESCALE_P##PASS); \
\
out5 = _mm_packs_pi32(out5l, out5h); \
out3 = _mm_packs_pi32(out3l, out3h); \
}
#define DO_FDCT_PASS1() { \
__m64 row0l, row0h, row1l, row1h, row2l, row2h, row3l, row3h; \
__m64 row01a, row01b, row01c, row01d, row23a, row23b, row23c, row23d; \
__m64 col0, col1, col2, col3, col4, col5, col6, col7; \
__m64 tmp10, tmp11; \
\
row0l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 0]); /* (00 01 02 03) */ \
row0h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 0 + 4]); /* (04 05 06 07) */ \
row1l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 1]); /* (10 11 12 13) */ \
row1h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 1 + 4]); /* (14 15 16 17) */ \
row2l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 2]); /* (20 21 22 23) */ \
row2h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 2 + 4]); /* (24 25 26 27) */ \
row3l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 3]); /* (30 31 32 33) */ \
row3h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 3 + 4]); /* (34 35 36 37) */ \
\
/* Transpose coefficients */ \
\
row23a = _mm_unpacklo_pi16(row2l, row3l); /* row23a=(20 30 21 31) */ \
row23b = _mm_unpackhi_pi16(row2l, row3l); /* row23b=(22 32 23 33) */ \
row23c = _mm_unpacklo_pi16(row2h, row3h); /* row23c=(24 34 25 35) */ \
row23d = _mm_unpackhi_pi16(row2h, row3h); /* row23d=(26 36 27 37) */ \
\
row01a = _mm_unpacklo_pi16(row0l, row1l); /* row01a=(00 10 01 11) */ \
row01b = _mm_unpackhi_pi16(row0l, row1l); /* row01b=(02 12 03 13) */ \
row01c = _mm_unpacklo_pi16(row0h, row1h); /* row01c=(04 14 05 15) */ \
row01d = _mm_unpackhi_pi16(row0h, row1h); /* row01d=(06 16 07 17) */ \
\
col0 = _mm_unpacklo_pi32(row01a, row23a); /* col0=(00 10 20 30) */ \
col1 = _mm_unpackhi_pi32(row01a, row23a); /* col1=(01 11 21 31) */ \
col6 = _mm_unpacklo_pi32(row01d, row23d); /* col6=(06 16 26 36) */ \
col7 = _mm_unpackhi_pi32(row01d, row23d); /* col7=(07 17 27 37) */ \
\
tmp6 = _mm_sub_pi16(col1, col6); /* tmp6=col1-col6 */ \
tmp7 = _mm_sub_pi16(col0, col7); /* tmp7=col0-col7 */ \
tmp1 = _mm_add_pi16(col1, col6); /* tmp1=col1+col6 */ \
tmp0 = _mm_add_pi16(col0, col7); /* tmp0=col0+col7 */ \
\
col2 = _mm_unpacklo_pi32(row01b, row23b); /* col2=(02 12 22 32) */ \
col3 = _mm_unpackhi_pi32(row01b, row23b); /* col3=(03 13 23 33) */ \
col4 = _mm_unpacklo_pi32(row01c, row23c); /* col4=(04 14 24 34) */ \
col5 = _mm_unpackhi_pi32(row01c, row23c); /* col5=(05 15 25 35) */ \
\
tmp3 = _mm_add_pi16(col3, col4); /* tmp3=col3+col4 */ \
tmp2 = _mm_add_pi16(col2, col5); /* tmp2=col2+col5 */ \
tmp4 = _mm_sub_pi16(col3, col4); /* tmp4=col3-col4 */ \
tmp5 = _mm_sub_pi16(col2, col5); /* tmp5=col2-col5 */ \
\
/* Even part */ \
\
tmp10 = _mm_add_pi16(tmp0, tmp3); /* tmp10=tmp0+tmp3 */ \
tmp13 = _mm_sub_pi16(tmp0, tmp3); /* tmp13=tmp0-tmp3 */ \
tmp11 = _mm_add_pi16(tmp1, tmp2); /* tmp11=tmp1+tmp2 */ \
tmp12 = _mm_sub_pi16(tmp1, tmp2); /* tmp12=tmp1-tmp2 */ \
\
out0 = _mm_add_pi16(tmp10, tmp11); /* out0=tmp10+tmp11 */ \
out4 = _mm_sub_pi16(tmp10, tmp11); /* out4=tmp10-tmp11 */ \
out0 = _mm_slli_pi16(out0, PASS1_BITS); \
out4 = _mm_slli_pi16(out4, PASS1_BITS); \
\
DO_FDCT_COMMON(1) \
\
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 0], out0); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 0 + 4], out4); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 1], out1); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 1 + 4], out5); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 2], out2); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 2 + 4], out6); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 3], out3); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 3 + 4], out7); \
}
#define DO_FDCT_PASS2() { \
__m64 col0l, col0h, col1l, col1h, col2l, col2h, col3l, col3h; \
__m64 col01a, col01b, col01c, col01d, col23a, col23b, col23c, col23d; \
__m64 row0, row1, row2, row3, row4, row5, row6, row7; \
__m64 tmp10, tmp11; \
\
col0l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 0]); /* (00 10 20 30) */ \
col1l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 1]); /* (01 11 21 31) */ \
col2l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 2]); /* (02 12 22 32) */ \
col3l = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 3]); /* (03 13 23 33) */ \
col0h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 4]); /* (40 50 60 70) */ \
col1h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 5]); /* (41 51 61 71) */ \
col2h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 6]); /* (42 52 62 72) */ \
col3h = _mm_load_si64((__m64 *)&dataptr[DCTSIZE * 7]); /* (43 53 63 73) */ \
\
/* Transpose coefficients */ \
\
col23a = _mm_unpacklo_pi16(col2l, col3l); /* col23a=(02 03 12 13) */ \
col23b = _mm_unpackhi_pi16(col2l, col3l); /* col23b=(22 23 32 33) */ \
col23c = _mm_unpacklo_pi16(col2h, col3h); /* col23c=(42 43 52 53) */ \
col23d = _mm_unpackhi_pi16(col2h, col3h); /* col23d=(62 63 72 73) */ \
\
col01a = _mm_unpacklo_pi16(col0l, col1l); /* col01a=(00 01 10 11) */ \
col01b = _mm_unpackhi_pi16(col0l, col1l); /* col01b=(20 21 30 31) */ \
col01c = _mm_unpacklo_pi16(col0h, col1h); /* col01c=(40 41 50 51) */ \
col01d = _mm_unpackhi_pi16(col0h, col1h); /* col01d=(60 61 70 71) */ \
\
row0 = _mm_unpacklo_pi32(col01a, col23a); /* row0=(00 01 02 03) */ \
row1 = _mm_unpackhi_pi32(col01a, col23a); /* row1=(10 11 12 13) */ \
row6 = _mm_unpacklo_pi32(col01d, col23d); /* row6=(60 61 62 63) */ \
row7 = _mm_unpackhi_pi32(col01d, col23d); /* row7=(70 71 72 73) */ \
\
tmp6 = _mm_sub_pi16(row1, row6); /* tmp6=row1-row6 */ \
tmp7 = _mm_sub_pi16(row0, row7); /* tmp7=row0-row7 */ \
tmp1 = _mm_add_pi16(row1, row6); /* tmp1=row1+row6 */ \
tmp0 = _mm_add_pi16(row0, row7); /* tmp0=row0+row7 */ \
\
row2 = _mm_unpacklo_pi32(col01b, col23b); /* row2=(20 21 22 23) */ \
row3 = _mm_unpackhi_pi32(col01b, col23b); /* row3=(30 31 32 33) */ \
row4 = _mm_unpacklo_pi32(col01c, col23c); /* row4=(40 41 42 43) */ \
row5 = _mm_unpackhi_pi32(col01c, col23c); /* row5=(50 51 52 53) */ \
\
tmp3 = _mm_add_pi16(row3, row4); /* tmp3=row3+row4 */ \
tmp2 = _mm_add_pi16(row2, row5); /* tmp2=row2+row5 */ \
tmp4 = _mm_sub_pi16(row3, row4); /* tmp4=row3-row4 */ \
tmp5 = _mm_sub_pi16(row2, row5); /* tmp5=row2-row5 */ \
\
/* Even part */ \
\
tmp10 = _mm_add_pi16(tmp0, tmp3); /* tmp10=tmp0+tmp3 */ \
tmp13 = _mm_sub_pi16(tmp0, tmp3); /* tmp13=tmp0-tmp3 */ \
tmp11 = _mm_add_pi16(tmp1, tmp2); /* tmp11=tmp1+tmp2 */ \
tmp12 = _mm_sub_pi16(tmp1, tmp2); /* tmp12=tmp1-tmp2 */ \
\
out0 = _mm_add_pi16(tmp10, tmp11); /* out0=tmp10+tmp11 */ \
out4 = _mm_sub_pi16(tmp10, tmp11); /* out4=tmp10-tmp11 */ \
\
out0 = _mm_add_pi16(out0, PW_DESCALE_P2X); \
out4 = _mm_add_pi16(out4, PW_DESCALE_P2X); \
out0 = _mm_srai_pi16(out0, PASS1_BITS); \
out4 = _mm_srai_pi16(out4, PASS1_BITS); \
\
DO_FDCT_COMMON(2) \
\
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 0], out0); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 1], out1); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 2], out2); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 3], out3); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 4], out4); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 5], out5); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 6], out6); \
_mm_store_si64((__m64 *)&dataptr[DCTSIZE * 7], out7); \
}
void jsimd_fdct_islow_mmi(DCTELEM *data)
{
__m64 tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
__m64 out0, out1, out2, out3, out4, out5, out6, out7;
__m64 tmp12, tmp13;
DCTELEM *dataptr = data;
/* Pass 1: process rows. */
DO_FDCT_PASS1()
dataptr += DCTSIZE * 4;
DO_FDCT_PASS1()
/* Pass 2: process columns. */
dataptr = data;
DO_FDCT_PASS2()
dataptr += 4;
DO_FDCT_PASS2()
}