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table-less version of clip_8b()

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added some dynamic range analysis too.

Change-Id: I76804adbfceccd83639c5821b4f0f5b9e7d6c82c
This commit is contained in:
Pascal Massimino 2010-12-17 05:56:37 -08:00
parent d72180a489
commit 1e0a2d25f6
1 changed files with 16 additions and 11 deletions
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27
src/dsp.c
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@ -51,8 +51,7 @@ void VP8DspInitTables() {
}
static inline uint8_t clip_8b(int v) {
assert(v >= -255 && v <= 255 + 255);
return clip1[255 + v];
return (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
}
//-----------------------------------------------------------------------------
@ -70,18 +69,24 @@ static void Transform(const int16_t* in, uint8_t* dst) {
int i;
tmp = C;
for (i = 0; i < 4; ++i) { // vertical pass
const int a = in[0] + in[8];
const int b = in[0] - in[8];
const int c = MUL(in[4], kC2) - MUL(in[12], kC1);
const int d = MUL(in[4], kC1) + MUL(in[12], kC2);
tmp[0] = a + d;
tmp[1] = b + c;
tmp[2] = b - c;
tmp[3] = a - d;
const int a = in[0] + in[8]; // [-4096, 4094]
const int b = in[0] - in[8]; // [-4095, 4095]
const int c = MUL(in[4], kC2) - MUL(in[12], kC1); // [-3783, 3783]
const int d = MUL(in[4], kC1) + MUL(in[12], kC2); // [-3785, 3781]
tmp[0] = a + d; // [-7881, 7875]
tmp[1] = b + c; // [-7878, 7878]
tmp[2] = b - c; // [-7878, 7878]
tmp[3] = a - d; // [-7877, 7879]
tmp += 4;
in++;
}
// Each pass is expanding the dynamic range by ~3.85 (upper bound).
// The exact value is (2. + (kC1 + kC2) / 65536).
// After the second pass, maximum interval is [-3794, 3794], assuming
// an input in [-2048, 2047] interval. We then need to add a dst value
// in the [0, 255] range.
// In the worst case scenario, the input to clip_8b() can be as large as
// [-60713, 60968].
tmp = C;
for (i = 0; i < 4; ++i) { // horizontal pass
const int dc = tmp[0] + 4;