| /* |
| * jfdctfst.c |
| * |
| * This file was part of the Independent JPEG Group's software: |
| * Copyright (C) 1994-1996, Thomas G. Lane. |
| * libjpeg-turbo Modifications: |
| * Copyright (C) 2015, D. R. Commander. |
| * For conditions of distribution and use, see the accompanying README.ijg |
| * file. |
| * |
| * This file contains a fast, not so accurate integer implementation of the |
| * forward DCT (Discrete Cosine Transform). |
| * |
| * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT |
| * on each column. Direct algorithms are also available, but they are |
| * much more complex and seem not to be any faster when reduced to code. |
| * |
| * This implementation is based on Arai, Agui, and Nakajima's algorithm for |
| * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in |
| * Japanese, but the algorithm is described in the Pennebaker & Mitchell |
| * JPEG textbook (see REFERENCES section in file README.ijg). The following |
| * code is based directly on figure 4-8 in P&M. |
| * While an 8-point DCT cannot be done in less than 11 multiplies, it is |
| * possible to arrange the computation so that many of the multiplies are |
| * simple scalings of the final outputs. These multiplies can then be |
| * folded into the multiplications or divisions by the JPEG quantization |
| * table entries. The AA&N method leaves only 5 multiplies and 29 adds |
| * to be done in the DCT itself. |
| * The primary disadvantage of this method is that with fixed-point math, |
| * accuracy is lost due to imprecise representation of the scaled |
| * quantization values. The smaller the quantization table entry, the less |
| * precise the scaled value, so this implementation does worse with high- |
| * quality-setting files than with low-quality ones. |
| */ |
| |
| #define JPEG_INTERNALS |
| #include "jinclude.h" |
| #include "jpeglib.h" |
| #include "jdct.h" /* Private declarations for DCT subsystem */ |
| |
| #ifdef DCT_IFAST_SUPPORTED |
| |
| |
| /* |
| * This module is specialized to the case DCTSIZE = 8. |
| */ |
| |
| #if DCTSIZE != 8 |
| Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ |
| #endif |
| |
| |
| /* Scaling decisions are generally the same as in the LL&M algorithm; |
| * see jfdctint.c for more details. However, we choose to descale |
| * (right shift) multiplication products as soon as they are formed, |
| * rather than carrying additional fractional bits into subsequent additions. |
| * This compromises accuracy slightly, but it lets us save a few shifts. |
| * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples) |
| * everywhere except in the multiplications proper; this saves a good deal |
| * of work on 16-bit-int machines. |
| * |
| * Again to save a few shifts, the intermediate results between pass 1 and |
| * pass 2 are not upscaled, but are represented only to integral precision. |
| * |
| * A final compromise is to represent the multiplicative constants to only |
| * 8 fractional bits, rather than 13. This saves some shifting work on some |
| * machines, and may also reduce the cost of multiplication (since there |
| * are fewer one-bits in the constants). |
| */ |
| |
| #define CONST_BITS 8 |
| |
| |
| /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus |
| * causing a lot of useless floating-point operations at run time. |
| * To get around this we use the following pre-calculated constants. |
| * If you change CONST_BITS you may want to add appropriate values. |
| * (With a reasonable C compiler, you can just rely on the FIX() macro...) |
| */ |
| |
| #if CONST_BITS == 8 |
| #define FIX_0_382683433 ((JLONG)98) /* FIX(0.382683433) */ |
| #define FIX_0_541196100 ((JLONG)139) /* FIX(0.541196100) */ |
| #define FIX_0_707106781 ((JLONG)181) /* FIX(0.707106781) */ |
| #define FIX_1_306562965 ((JLONG)334) /* FIX(1.306562965) */ |
| #else |
| #define FIX_0_382683433 FIX(0.382683433) |
| #define FIX_0_541196100 FIX(0.541196100) |
| #define FIX_0_707106781 FIX(0.707106781) |
| #define FIX_1_306562965 FIX(1.306562965) |
| #endif |
| |
| |
| /* We can gain a little more speed, with a further compromise in accuracy, |
| * by omitting the addition in a descaling shift. This yields an incorrectly |
| * rounded result half the time... |
| */ |
| |
| #ifndef USE_ACCURATE_ROUNDING |
| #undef DESCALE |
| #define DESCALE(x, n) RIGHT_SHIFT(x, n) |
| #endif |
| |
| |
| /* Multiply a DCTELEM variable by an JLONG constant, and immediately |
| * descale to yield a DCTELEM result. |
| */ |
| |
| #define MULTIPLY(var, const) ((DCTELEM)DESCALE((var) * (const), CONST_BITS)) |
| |
| |
| /* |
| * Perform the forward DCT on one block of samples. |
| */ |
| |
| GLOBAL(void) |
| _jpeg_fdct_ifast(DCTELEM *data) |
| { |
| DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; |
| DCTELEM tmp10, tmp11, tmp12, tmp13; |
| DCTELEM z1, z2, z3, z4, z5, z11, z13; |
| DCTELEM *dataptr; |
| int ctr; |
| SHIFT_TEMPS |
| |
| /* Pass 1: process rows. */ |
| |
| dataptr = data; |
| for (ctr = DCTSIZE - 1; ctr >= 0; ctr--) { |
| tmp0 = dataptr[0] + dataptr[7]; |
| tmp7 = dataptr[0] - dataptr[7]; |
| tmp1 = dataptr[1] + dataptr[6]; |
| tmp6 = dataptr[1] - dataptr[6]; |
| tmp2 = dataptr[2] + dataptr[5]; |
| tmp5 = dataptr[2] - dataptr[5]; |
| tmp3 = dataptr[3] + dataptr[4]; |
| tmp4 = dataptr[3] - dataptr[4]; |
| |
| /* Even part */ |
| |
| tmp10 = tmp0 + tmp3; /* phase 2 */ |
| tmp13 = tmp0 - tmp3; |
| tmp11 = tmp1 + tmp2; |
| tmp12 = tmp1 - tmp2; |
| |
| dataptr[0] = tmp10 + tmp11; /* phase 3 */ |
| dataptr[4] = tmp10 - tmp11; |
| |
| z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */ |
| dataptr[2] = tmp13 + z1; /* phase 5 */ |
| dataptr[6] = tmp13 - z1; |
| |
| /* Odd part */ |
| |
| tmp10 = tmp4 + tmp5; /* phase 2 */ |
| tmp11 = tmp5 + tmp6; |
| tmp12 = tmp6 + tmp7; |
| |
| /* The rotator is modified from fig 4-8 to avoid extra negations. */ |
| z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */ |
| z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */ |
| z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */ |
| z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */ |
| |
| z11 = tmp7 + z3; /* phase 5 */ |
| z13 = tmp7 - z3; |
| |
| dataptr[5] = z13 + z2; /* phase 6 */ |
| dataptr[3] = z13 - z2; |
| dataptr[1] = z11 + z4; |
| dataptr[7] = z11 - z4; |
| |
| dataptr += DCTSIZE; /* advance pointer to next row */ |
| } |
| |
| /* Pass 2: process columns. */ |
| |
| dataptr = data; |
| for (ctr = DCTSIZE - 1; ctr >= 0; ctr--) { |
| tmp0 = dataptr[DCTSIZE * 0] + dataptr[DCTSIZE * 7]; |
| tmp7 = dataptr[DCTSIZE * 0] - dataptr[DCTSIZE * 7]; |
| tmp1 = dataptr[DCTSIZE * 1] + dataptr[DCTSIZE * 6]; |
| tmp6 = dataptr[DCTSIZE * 1] - dataptr[DCTSIZE * 6]; |
| tmp2 = dataptr[DCTSIZE * 2] + dataptr[DCTSIZE * 5]; |
| tmp5 = dataptr[DCTSIZE * 2] - dataptr[DCTSIZE * 5]; |
| tmp3 = dataptr[DCTSIZE * 3] + dataptr[DCTSIZE * 4]; |
| tmp4 = dataptr[DCTSIZE * 3] - dataptr[DCTSIZE * 4]; |
| |
| /* Even part */ |
| |
| tmp10 = tmp0 + tmp3; /* phase 2 */ |
| tmp13 = tmp0 - tmp3; |
| tmp11 = tmp1 + tmp2; |
| tmp12 = tmp1 - tmp2; |
| |
| dataptr[DCTSIZE * 0] = tmp10 + tmp11; /* phase 3 */ |
| dataptr[DCTSIZE * 4] = tmp10 - tmp11; |
| |
| z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */ |
| dataptr[DCTSIZE * 2] = tmp13 + z1; /* phase 5 */ |
| dataptr[DCTSIZE * 6] = tmp13 - z1; |
| |
| /* Odd part */ |
| |
| tmp10 = tmp4 + tmp5; /* phase 2 */ |
| tmp11 = tmp5 + tmp6; |
| tmp12 = tmp6 + tmp7; |
| |
| /* The rotator is modified from fig 4-8 to avoid extra negations. */ |
| z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */ |
| z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */ |
| z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */ |
| z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */ |
| |
| z11 = tmp7 + z3; /* phase 5 */ |
| z13 = tmp7 - z3; |
| |
| dataptr[DCTSIZE * 5] = z13 + z2; /* phase 6 */ |
| dataptr[DCTSIZE * 3] = z13 - z2; |
| dataptr[DCTSIZE * 1] = z11 + z4; |
| dataptr[DCTSIZE * 7] = z11 - z4; |
| |
| dataptr++; /* advance pointer to next column */ |
| } |
| } |
| |
| #endif /* DCT_IFAST_SUPPORTED */ |