From fab3091cc16494d88aa32f033048542cdcc38197 Mon Sep 17 00:00:00 2001 From: "K. Lange" Date: Tue, 18 Dec 2018 19:33:21 +0900 Subject: [PATCH] jpeg: use a precalculated cosine table, which is about twice as fast --- lib/jpeg.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/lib/jpeg.c b/lib/jpeg.c index 6640579f..c60c7252 100644 --- a/lib/jpeg.c +++ b/lib/jpeg.c @@ -210,13 +210,24 @@ static double norm_coeff[2] = { 0.5, }; +static double cosines[8][8] = { + {1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0}, + {0.9807852804032304, 0.8314696123025452, 0.5555702330196023, 0.19509032201612833, -0.1950903220161282, -0.555570233019602, -0.8314696123025453, -0.9807852804032304}, + {0.9238795325112867, 0.38268343236508984, -0.3826834323650897, -0.9238795325112867, -0.9238795325112868, -0.38268343236509034, 0.38268343236509, 0.9238795325112865}, + {0.8314696123025452, -0.1950903220161282, -0.9807852804032304, -0.5555702330196022, 0.5555702330196018, 0.9807852804032304, 0.19509032201612878, -0.8314696123025451}, + {0.7071067811865476, -0.7071067811865475, -0.7071067811865477, 0.7071067811865474, 0.7071067811865477, -0.7071067811865467, -0.7071067811865471, 0.7071067811865466}, + {0.5555702330196023, -0.9807852804032304, 0.1950903220161283, 0.8314696123025455, -0.8314696123025451, -0.19509032201612803, 0.9807852804032307, -0.5555702330196015}, + {0.38268343236508984, -0.9238795325112868, 0.9238795325112865, -0.3826834323650899, -0.38268343236509056, 0.9238795325112867, -0.9238795325112864, 0.38268343236508956}, + {0.19509032201612833, -0.5555702330196022, 0.8314696123025455, -0.9807852804032307, 0.9807852804032304, -0.831469612302545, 0.5555702330196015, -0.19509032201612858}, +}; + static void add_idc(struct idct * self, int n, int m, int coeff) { double an = norm_coeff[!!n]; double am = norm_coeff[!!m]; for (int y = 0; y < 8; ++y) { for (int x = 0; x < 8; ++x) { - double nn = an * cos((double)n * M_PI * ((double)x + 0.5) / 8.0); - double mm = am * cos((double)m * M_PI * ((double)y + 0.5) / 8.0); + double nn = an * cosines[n][x]; // cos((double)n * M_PI * ((double)x + 0.5) / 8.0); + double mm = am * cosines[m][y]; // cos((double)m * M_PI * ((double)y + 0.5) / 8.0); self->base[xy_to_lin(x, y)] += nn * mm * coeff; } }