Take out assertion from inverse transforms
Separate the rounding and right shift operations of forward transform
from those of inverse transform. Take out the assertion check from
inverse transforms. If the transform coefficients were constructed to
cause intermediate steps of inverse transform overflow, the codec will
just let it overflow without breaking the decoding flow.
Change-Id: Ia7ce15dfd1a73b4abbaa78cbc74ec718523c5b1b
diff --git a/vp9/common/vp9_idct.h b/vp9/common/vp9_idct.h
index 2b3f35f..183c50a 100644
--- a/vp9/common/vp9_idct.h
+++ b/vp9/common/vp9_idct.h
@@ -77,8 +77,7 @@
static INLINE int dct_const_round_shift(int input) {
int rv = ROUND_POWER_OF_TWO(input, DCT_CONST_BITS);
- assert(INT16_MIN <= rv && rv <= INT16_MAX);
- return rv;
+ return (int16_t)rv;
}
typedef void (*transform_1d)(const int16_t*, int16_t*);
diff --git a/vp9/encoder/vp9_dct.c b/vp9/encoder/vp9_dct.c
index 065992a..0f4a6bb 100644
--- a/vp9/encoder/vp9_dct.c
+++ b/vp9/encoder/vp9_dct.c
@@ -20,6 +20,12 @@
#include "vp9/encoder/vp9_dct.h"
+static INLINE int fdct_round_shift(int input) {
+ int rv = ROUND_POWER_OF_TWO(input, DCT_CONST_BITS);
+ assert(INT16_MIN <= rv && rv <= INT16_MAX);
+ return rv;
+}
+
static void fdct4(const int16_t *input, int16_t *output) {
int16_t step[4];
int temp1, temp2;
@@ -31,12 +37,12 @@
temp1 = (step[0] + step[1]) * cospi_16_64;
temp2 = (step[0] - step[1]) * cospi_16_64;
- output[0] = dct_const_round_shift(temp1);
- output[2] = dct_const_round_shift(temp2);
+ output[0] = fdct_round_shift(temp1);
+ output[2] = fdct_round_shift(temp2);
temp1 = step[2] * cospi_24_64 + step[3] * cospi_8_64;
temp2 = -step[2] * cospi_8_64 + step[3] * cospi_24_64;
- output[1] = dct_const_round_shift(temp1);
- output[3] = dct_const_round_shift(temp2);
+ output[1] = fdct_round_shift(temp1);
+ output[3] = fdct_round_shift(temp2);
}
void vp9_fdct4x4_c(const int16_t *input, int16_t *output, int stride) {
@@ -80,12 +86,12 @@
step[3] = input[0] - input[3];
temp1 = (step[0] + step[1]) * cospi_16_64;
temp2 = (step[0] - step[1]) * cospi_16_64;
- out[0] = dct_const_round_shift(temp1);
- out[2] = dct_const_round_shift(temp2);
+ out[0] = fdct_round_shift(temp1);
+ out[2] = fdct_round_shift(temp2);
temp1 = step[2] * cospi_24_64 + step[3] * cospi_8_64;
temp2 = -step[2] * cospi_8_64 + step[3] * cospi_24_64;
- out[1] = dct_const_round_shift(temp1);
- out[3] = dct_const_round_shift(temp2);
+ out[1] = fdct_round_shift(temp1);
+ out[3] = fdct_round_shift(temp2);
// Do next column (which is a transposed row in second/horizontal pass)
in++;
out += 4;
@@ -138,10 +144,10 @@
s3 = x2 - x0 + x3;
// 1-D transform scaling factor is sqrt(2).
- output[0] = dct_const_round_shift(s0);
- output[1] = dct_const_round_shift(s1);
- output[2] = dct_const_round_shift(s2);
- output[3] = dct_const_round_shift(s3);
+ output[0] = fdct_round_shift(s0);
+ output[1] = fdct_round_shift(s1);
+ output[2] = fdct_round_shift(s2);
+ output[3] = fdct_round_shift(s3);
}
static const transform_2d FHT_4[] = {
@@ -204,16 +210,16 @@
t1 = (x0 - x1) * cospi_16_64;
t2 = x2 * cospi_24_64 + x3 * cospi_8_64;
t3 = -x2 * cospi_8_64 + x3 * cospi_24_64;
- output[0] = dct_const_round_shift(t0);
- output[2] = dct_const_round_shift(t2);
- output[4] = dct_const_round_shift(t1);
- output[6] = dct_const_round_shift(t3);
+ output[0] = fdct_round_shift(t0);
+ output[2] = fdct_round_shift(t2);
+ output[4] = fdct_round_shift(t1);
+ output[6] = fdct_round_shift(t3);
// Stage 2
t0 = (s6 - s5) * cospi_16_64;
t1 = (s6 + s5) * cospi_16_64;
- t2 = dct_const_round_shift(t0);
- t3 = dct_const_round_shift(t1);
+ t2 = fdct_round_shift(t0);
+ t3 = fdct_round_shift(t1);
// Stage 3
x0 = s4 + t2;
@@ -226,10 +232,10 @@
t1 = x1 * cospi_12_64 + x2 * cospi_20_64;
t2 = x2 * cospi_12_64 + x1 * -cospi_20_64;
t3 = x3 * cospi_28_64 + x0 * -cospi_4_64;
- output[1] = dct_const_round_shift(t0);
- output[3] = dct_const_round_shift(t2);
- output[5] = dct_const_round_shift(t1);
- output[7] = dct_const_round_shift(t3);
+ output[1] = fdct_round_shift(t0);
+ output[3] = fdct_round_shift(t2);
+ output[5] = fdct_round_shift(t1);
+ output[7] = fdct_round_shift(t3);
}
void vp9_fdct8x8_c(const int16_t *input, int16_t *final_output, int stride) {
@@ -264,16 +270,16 @@
t1 = (x0 - x1) * cospi_16_64;
t2 = x2 * cospi_24_64 + x3 * cospi_8_64;
t3 = -x2 * cospi_8_64 + x3 * cospi_24_64;
- output[0 * 8] = dct_const_round_shift(t0);
- output[2 * 8] = dct_const_round_shift(t2);
- output[4 * 8] = dct_const_round_shift(t1);
- output[6 * 8] = dct_const_round_shift(t3);
+ output[0 * 8] = fdct_round_shift(t0);
+ output[2 * 8] = fdct_round_shift(t2);
+ output[4 * 8] = fdct_round_shift(t1);
+ output[6 * 8] = fdct_round_shift(t3);
// Stage 2
t0 = (s6 - s5) * cospi_16_64;
t1 = (s6 + s5) * cospi_16_64;
- t2 = dct_const_round_shift(t0);
- t3 = dct_const_round_shift(t1);
+ t2 = fdct_round_shift(t0);
+ t3 = fdct_round_shift(t1);
// Stage 3
x0 = s4 + t2;
@@ -286,10 +292,10 @@
t1 = x1 * cospi_12_64 + x2 * cospi_20_64;
t2 = x2 * cospi_12_64 + x1 * -cospi_20_64;
t3 = x3 * cospi_28_64 + x0 * -cospi_4_64;
- output[1 * 8] = dct_const_round_shift(t0);
- output[3 * 8] = dct_const_round_shift(t2);
- output[5 * 8] = dct_const_round_shift(t1);
- output[7 * 8] = dct_const_round_shift(t3);
+ output[1 * 8] = fdct_round_shift(t0);
+ output[3 * 8] = fdct_round_shift(t2);
+ output[5 * 8] = fdct_round_shift(t1);
+ output[7 * 8] = fdct_round_shift(t3);
input++;
output++;
}
@@ -388,16 +394,16 @@
t1 = (x0 - x1) * cospi_16_64;
t2 = x3 * cospi_8_64 + x2 * cospi_24_64;
t3 = x3 * cospi_24_64 - x2 * cospi_8_64;
- out[0] = dct_const_round_shift(t0);
- out[4] = dct_const_round_shift(t2);
- out[8] = dct_const_round_shift(t1);
- out[12] = dct_const_round_shift(t3);
+ out[0] = fdct_round_shift(t0);
+ out[4] = fdct_round_shift(t2);
+ out[8] = fdct_round_shift(t1);
+ out[12] = fdct_round_shift(t3);
// Stage 2
t0 = (s6 - s5) * cospi_16_64;
t1 = (s6 + s5) * cospi_16_64;
- t2 = dct_const_round_shift(t0);
- t3 = dct_const_round_shift(t1);
+ t2 = fdct_round_shift(t0);
+ t3 = fdct_round_shift(t1);
// Stage 3
x0 = s4 + t2;
@@ -410,22 +416,22 @@
t1 = x1 * cospi_12_64 + x2 * cospi_20_64;
t2 = x2 * cospi_12_64 + x1 * -cospi_20_64;
t3 = x3 * cospi_28_64 + x0 * -cospi_4_64;
- out[2] = dct_const_round_shift(t0);
- out[6] = dct_const_round_shift(t2);
- out[10] = dct_const_round_shift(t1);
- out[14] = dct_const_round_shift(t3);
+ out[2] = fdct_round_shift(t0);
+ out[6] = fdct_round_shift(t2);
+ out[10] = fdct_round_shift(t1);
+ out[14] = fdct_round_shift(t3);
}
// Work on the next eight values; step1 -> odd_results
{
// step 2
temp1 = (step1[5] - step1[2]) * cospi_16_64;
temp2 = (step1[4] - step1[3]) * cospi_16_64;
- step2[2] = dct_const_round_shift(temp1);
- step2[3] = dct_const_round_shift(temp2);
+ step2[2] = fdct_round_shift(temp1);
+ step2[3] = fdct_round_shift(temp2);
temp1 = (step1[4] + step1[3]) * cospi_16_64;
temp2 = (step1[5] + step1[2]) * cospi_16_64;
- step2[4] = dct_const_round_shift(temp1);
- step2[5] = dct_const_round_shift(temp2);
+ step2[4] = fdct_round_shift(temp1);
+ step2[5] = fdct_round_shift(temp2);
// step 3
step3[0] = step1[0] + step2[3];
step3[1] = step1[1] + step2[2];
@@ -438,12 +444,12 @@
// step 4
temp1 = step3[1] * -cospi_8_64 + step3[6] * cospi_24_64;
temp2 = step3[2] * -cospi_24_64 - step3[5] * cospi_8_64;
- step2[1] = dct_const_round_shift(temp1);
- step2[2] = dct_const_round_shift(temp2);
+ step2[1] = fdct_round_shift(temp1);
+ step2[2] = fdct_round_shift(temp2);
temp1 = step3[2] * -cospi_8_64 + step3[5] * cospi_24_64;
temp2 = step3[1] * cospi_24_64 + step3[6] * cospi_8_64;
- step2[5] = dct_const_round_shift(temp1);
- step2[6] = dct_const_round_shift(temp2);
+ step2[5] = fdct_round_shift(temp1);
+ step2[6] = fdct_round_shift(temp2);
// step 5
step1[0] = step3[0] + step2[1];
step1[1] = step3[0] - step2[1];
@@ -456,20 +462,20 @@
// step 6
temp1 = step1[0] * cospi_30_64 + step1[7] * cospi_2_64;
temp2 = step1[1] * cospi_14_64 + step1[6] * cospi_18_64;
- out[1] = dct_const_round_shift(temp1);
- out[9] = dct_const_round_shift(temp2);
+ out[1] = fdct_round_shift(temp1);
+ out[9] = fdct_round_shift(temp2);
temp1 = step1[2] * cospi_22_64 + step1[5] * cospi_10_64;
temp2 = step1[3] * cospi_6_64 + step1[4] * cospi_26_64;
- out[5] = dct_const_round_shift(temp1);
- out[13] = dct_const_round_shift(temp2);
+ out[5] = fdct_round_shift(temp1);
+ out[13] = fdct_round_shift(temp2);
temp1 = step1[3] * -cospi_26_64 + step1[4] * cospi_6_64;
temp2 = step1[2] * -cospi_10_64 + step1[5] * cospi_22_64;
- out[3] = dct_const_round_shift(temp1);
- out[11] = dct_const_round_shift(temp2);
+ out[3] = fdct_round_shift(temp1);
+ out[11] = fdct_round_shift(temp2);
temp1 = step1[1] * -cospi_18_64 + step1[6] * cospi_14_64;
temp2 = step1[0] * -cospi_2_64 + step1[7] * cospi_30_64;
- out[7] = dct_const_round_shift(temp1);
- out[15] = dct_const_round_shift(temp2);
+ out[7] = fdct_round_shift(temp1);
+ out[15] = fdct_round_shift(temp2);
}
// Do next column (which is a transposed row in second/horizontal pass)
in++;
@@ -503,14 +509,14 @@
s6 = cospi_26_64 * x6 + cospi_6_64 * x7;
s7 = cospi_6_64 * x6 - cospi_26_64 * x7;
- x0 = dct_const_round_shift(s0 + s4);
- x1 = dct_const_round_shift(s1 + s5);
- x2 = dct_const_round_shift(s2 + s6);
- x3 = dct_const_round_shift(s3 + s7);
- x4 = dct_const_round_shift(s0 - s4);
- x5 = dct_const_round_shift(s1 - s5);
- x6 = dct_const_round_shift(s2 - s6);
- x7 = dct_const_round_shift(s3 - s7);
+ x0 = fdct_round_shift(s0 + s4);
+ x1 = fdct_round_shift(s1 + s5);
+ x2 = fdct_round_shift(s2 + s6);
+ x3 = fdct_round_shift(s3 + s7);
+ x4 = fdct_round_shift(s0 - s4);
+ x5 = fdct_round_shift(s1 - s5);
+ x6 = fdct_round_shift(s2 - s6);
+ x7 = fdct_round_shift(s3 - s7);
// stage 2
s0 = x0;
@@ -526,10 +532,10 @@
x1 = s1 + s3;
x2 = s0 - s2;
x3 = s1 - s3;
- x4 = dct_const_round_shift(s4 + s6);
- x5 = dct_const_round_shift(s5 + s7);
- x6 = dct_const_round_shift(s4 - s6);
- x7 = dct_const_round_shift(s5 - s7);
+ x4 = fdct_round_shift(s4 + s6);
+ x5 = fdct_round_shift(s5 + s7);
+ x6 = fdct_round_shift(s4 - s6);
+ x7 = fdct_round_shift(s5 - s7);
// stage 3
s2 = cospi_16_64 * (x2 + x3);
@@ -537,10 +543,10 @@
s6 = cospi_16_64 * (x6 + x7);
s7 = cospi_16_64 * (x6 - x7);
- x2 = dct_const_round_shift(s2);
- x3 = dct_const_round_shift(s3);
- x6 = dct_const_round_shift(s6);
- x7 = dct_const_round_shift(s7);
+ x2 = fdct_round_shift(s2);
+ x3 = fdct_round_shift(s3);
+ x6 = fdct_round_shift(s6);
+ x7 = fdct_round_shift(s7);
output[0] = x0;
output[1] = - x4;
@@ -693,16 +699,16 @@
t1 = (x0 - x1) * cospi_16_64;
t2 = x3 * cospi_8_64 + x2 * cospi_24_64;
t3 = x3 * cospi_24_64 - x2 * cospi_8_64;
- out[0] = dct_const_round_shift(t0);
- out[4] = dct_const_round_shift(t2);
- out[8] = dct_const_round_shift(t1);
- out[12] = dct_const_round_shift(t3);
+ out[0] = fdct_round_shift(t0);
+ out[4] = fdct_round_shift(t2);
+ out[8] = fdct_round_shift(t1);
+ out[12] = fdct_round_shift(t3);
// Stage 2
t0 = (s6 - s5) * cospi_16_64;
t1 = (s6 + s5) * cospi_16_64;
- t2 = dct_const_round_shift(t0);
- t3 = dct_const_round_shift(t1);
+ t2 = fdct_round_shift(t0);
+ t3 = fdct_round_shift(t1);
// Stage 3
x0 = s4 + t2;
@@ -715,21 +721,21 @@
t1 = x1 * cospi_12_64 + x2 * cospi_20_64;
t2 = x2 * cospi_12_64 + x1 * -cospi_20_64;
t3 = x3 * cospi_28_64 + x0 * -cospi_4_64;
- out[2] = dct_const_round_shift(t0);
- out[6] = dct_const_round_shift(t2);
- out[10] = dct_const_round_shift(t1);
- out[14] = dct_const_round_shift(t3);
+ out[2] = fdct_round_shift(t0);
+ out[6] = fdct_round_shift(t2);
+ out[10] = fdct_round_shift(t1);
+ out[14] = fdct_round_shift(t3);
}
// step 2
temp1 = (step1[5] - step1[2]) * cospi_16_64;
temp2 = (step1[4] - step1[3]) * cospi_16_64;
- step2[2] = dct_const_round_shift(temp1);
- step2[3] = dct_const_round_shift(temp2);
+ step2[2] = fdct_round_shift(temp1);
+ step2[3] = fdct_round_shift(temp2);
temp1 = (step1[4] + step1[3]) * cospi_16_64;
temp2 = (step1[5] + step1[2]) * cospi_16_64;
- step2[4] = dct_const_round_shift(temp1);
- step2[5] = dct_const_round_shift(temp2);
+ step2[4] = fdct_round_shift(temp1);
+ step2[5] = fdct_round_shift(temp2);
// step 3
step3[0] = step1[0] + step2[3];
@@ -744,12 +750,12 @@
// step 4
temp1 = step3[1] * -cospi_8_64 + step3[6] * cospi_24_64;
temp2 = step3[2] * -cospi_24_64 - step3[5] * cospi_8_64;
- step2[1] = dct_const_round_shift(temp1);
- step2[2] = dct_const_round_shift(temp2);
+ step2[1] = fdct_round_shift(temp1);
+ step2[2] = fdct_round_shift(temp2);
temp1 = step3[2] * -cospi_8_64 + step3[5] * cospi_24_64;
temp2 = step3[1] * cospi_24_64 + step3[6] * cospi_8_64;
- step2[5] = dct_const_round_shift(temp1);
- step2[6] = dct_const_round_shift(temp2);
+ step2[5] = fdct_round_shift(temp1);
+ step2[6] = fdct_round_shift(temp2);
// step 5
step1[0] = step3[0] + step2[1];
@@ -764,23 +770,23 @@
// step 6
temp1 = step1[0] * cospi_30_64 + step1[7] * cospi_2_64;
temp2 = step1[1] * cospi_14_64 + step1[6] * cospi_18_64;
- out[1] = dct_const_round_shift(temp1);
- out[9] = dct_const_round_shift(temp2);
+ out[1] = fdct_round_shift(temp1);
+ out[9] = fdct_round_shift(temp2);
temp1 = step1[2] * cospi_22_64 + step1[5] * cospi_10_64;
temp2 = step1[3] * cospi_6_64 + step1[4] * cospi_26_64;
- out[5] = dct_const_round_shift(temp1);
- out[13] = dct_const_round_shift(temp2);
+ out[5] = fdct_round_shift(temp1);
+ out[13] = fdct_round_shift(temp2);
temp1 = step1[3] * -cospi_26_64 + step1[4] * cospi_6_64;
temp2 = step1[2] * -cospi_10_64 + step1[5] * cospi_22_64;
- out[3] = dct_const_round_shift(temp1);
- out[11] = dct_const_round_shift(temp2);
+ out[3] = fdct_round_shift(temp1);
+ out[11] = fdct_round_shift(temp2);
temp1 = step1[1] * -cospi_18_64 + step1[6] * cospi_14_64;
temp2 = step1[0] * -cospi_2_64 + step1[7] * cospi_30_64;
- out[7] = dct_const_round_shift(temp1);
- out[15] = dct_const_round_shift(temp2);
+ out[7] = fdct_round_shift(temp1);
+ out[15] = fdct_round_shift(temp2);
}
static void fadst16(const int16_t *input, int16_t *output) {
@@ -821,22 +827,22 @@
s14 = x14 * cospi_29_64 + x15 * cospi_3_64;
s15 = x14 * cospi_3_64 - x15 * cospi_29_64;
- x0 = dct_const_round_shift(s0 + s8);
- x1 = dct_const_round_shift(s1 + s9);
- x2 = dct_const_round_shift(s2 + s10);
- x3 = dct_const_round_shift(s3 + s11);
- x4 = dct_const_round_shift(s4 + s12);
- x5 = dct_const_round_shift(s5 + s13);
- x6 = dct_const_round_shift(s6 + s14);
- x7 = dct_const_round_shift(s7 + s15);
- x8 = dct_const_round_shift(s0 - s8);
- x9 = dct_const_round_shift(s1 - s9);
- x10 = dct_const_round_shift(s2 - s10);
- x11 = dct_const_round_shift(s3 - s11);
- x12 = dct_const_round_shift(s4 - s12);
- x13 = dct_const_round_shift(s5 - s13);
- x14 = dct_const_round_shift(s6 - s14);
- x15 = dct_const_round_shift(s7 - s15);
+ x0 = fdct_round_shift(s0 + s8);
+ x1 = fdct_round_shift(s1 + s9);
+ x2 = fdct_round_shift(s2 + s10);
+ x3 = fdct_round_shift(s3 + s11);
+ x4 = fdct_round_shift(s4 + s12);
+ x5 = fdct_round_shift(s5 + s13);
+ x6 = fdct_round_shift(s6 + s14);
+ x7 = fdct_round_shift(s7 + s15);
+ x8 = fdct_round_shift(s0 - s8);
+ x9 = fdct_round_shift(s1 - s9);
+ x10 = fdct_round_shift(s2 - s10);
+ x11 = fdct_round_shift(s3 - s11);
+ x12 = fdct_round_shift(s4 - s12);
+ x13 = fdct_round_shift(s5 - s13);
+ x14 = fdct_round_shift(s6 - s14);
+ x15 = fdct_round_shift(s7 - s15);
// stage 2
s0 = x0;
@@ -864,14 +870,14 @@
x5 = s1 - s5;
x6 = s2 - s6;
x7 = s3 - s7;
- x8 = dct_const_round_shift(s8 + s12);
- x9 = dct_const_round_shift(s9 + s13);
- x10 = dct_const_round_shift(s10 + s14);
- x11 = dct_const_round_shift(s11 + s15);
- x12 = dct_const_round_shift(s8 - s12);
- x13 = dct_const_round_shift(s9 - s13);
- x14 = dct_const_round_shift(s10 - s14);
- x15 = dct_const_round_shift(s11 - s15);
+ x8 = fdct_round_shift(s8 + s12);
+ x9 = fdct_round_shift(s9 + s13);
+ x10 = fdct_round_shift(s10 + s14);
+ x11 = fdct_round_shift(s11 + s15);
+ x12 = fdct_round_shift(s8 - s12);
+ x13 = fdct_round_shift(s9 - s13);
+ x14 = fdct_round_shift(s10 - s14);
+ x15 = fdct_round_shift(s11 - s15);
// stage 3
s0 = x0;
@@ -895,18 +901,18 @@
x1 = s1 + s3;
x2 = s0 - s2;
x3 = s1 - s3;
- x4 = dct_const_round_shift(s4 + s6);
- x5 = dct_const_round_shift(s5 + s7);
- x6 = dct_const_round_shift(s4 - s6);
- x7 = dct_const_round_shift(s5 - s7);
+ x4 = fdct_round_shift(s4 + s6);
+ x5 = fdct_round_shift(s5 + s7);
+ x6 = fdct_round_shift(s4 - s6);
+ x7 = fdct_round_shift(s5 - s7);
x8 = s8 + s10;
x9 = s9 + s11;
x10 = s8 - s10;
x11 = s9 - s11;
- x12 = dct_const_round_shift(s12 + s14);
- x13 = dct_const_round_shift(s13 + s15);
- x14 = dct_const_round_shift(s12 - s14);
- x15 = dct_const_round_shift(s13 - s15);
+ x12 = fdct_round_shift(s12 + s14);
+ x13 = fdct_round_shift(s13 + s15);
+ x14 = fdct_round_shift(s12 - s14);
+ x15 = fdct_round_shift(s13 - s15);
// stage 4
s2 = (- cospi_16_64) * (x2 + x3);
@@ -918,14 +924,14 @@
s14 = (- cospi_16_64) * (x14 + x15);
s15 = cospi_16_64 * (x14 - x15);
- x2 = dct_const_round_shift(s2);
- x3 = dct_const_round_shift(s3);
- x6 = dct_const_round_shift(s6);
- x7 = dct_const_round_shift(s7);
- x10 = dct_const_round_shift(s10);
- x11 = dct_const_round_shift(s11);
- x14 = dct_const_round_shift(s14);
- x15 = dct_const_round_shift(s15);
+ x2 = fdct_round_shift(s2);
+ x3 = fdct_round_shift(s3);
+ x6 = fdct_round_shift(s6);
+ x7 = fdct_round_shift(s7);
+ x10 = fdct_round_shift(s10);
+ x11 = fdct_round_shift(s11);
+ x14 = fdct_round_shift(s14);
+ x15 = fdct_round_shift(s15);
output[0] = x0;
output[1] = - x8;
