From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Tue, 10 Oct 2017 16:04:07 +0000 (+0200)
Subject: Start trying to count the rANS distributions from the encoding shader.
X-Git-Url: https://git.sesse.net/?p=narabu;a=commitdiff_plain;h=fb687c35b84f1376293338d1d88a7ed99eb80421

Start trying to count the rANS distributions from the encoding shader.
---

diff --git a/coded.dat b/coded.dat
index e94ba8c..469306f 100644
Binary files a/coded.dat and b/coded.dat differ
diff --git a/encoder.shader b/encoder.shader
index dc17453..da9e6c0 100644
--- a/encoder.shader
+++ b/encoder.shader
@@ -12,6 +12,24 @@ layout(r8ui) uniform restrict readonly uimage2D image_tex;
 
 shared float temp[64];
 
+layout(std430, binding = 9) buffer layoutName
+{
+	uint dist[4][256];
+};
+
+#define MAPPING(s0, s1, s2, s3, s4, s5, s6, s7) ((s0) | (s1 << 2) | (s2 << 4) | (s3 << 6) | (s4 << 8) | (s5 << 10) | (s6 << 12) | (s7 << 14))
+
+const uint luma_mapping[8] = {
+	MAPPING(0, 0, 1, 1, 2, 2, 3, 3),
+	MAPPING(0, 0, 1, 2, 2, 2, 3, 3),
+	MAPPING(1, 1, 2, 2, 2, 3, 3, 3),
+	MAPPING(1, 1, 2, 2, 2, 3, 3, 3),
+	MAPPING(1, 2, 2, 2, 2, 3, 3, 3),
+	MAPPING(2, 2, 2, 2, 3, 3, 3, 3),
+	MAPPING(2, 2, 3, 3, 3, 3, 3, 3),
+	MAPPING(3, 3, 3, 3, 3, 3, 3, 3),
+};
+
 // Scale factors; 1.0 / (sqrt(2.0) * cos(k * M_PI / 16.0)), except for the first which is 1.
 const float sf[8] = {
 	1.0, 0.7209598220069479, 0.765366864730180, 0.8504300947672564,
@@ -166,5 +184,39 @@ void main()
 	imageStore(ac2_ac5_tex, ivec2(sx, y + n), uvec4(pack_9_7(c2, c5), 0, 0, 0));
 	imageStore(ac3_tex,     ivec2(sx, y + n), ivec4(c3, 0, 0, 0));
 	imageStore(ac4_tex,     ivec2(sx, y + n), ivec4(c4, 0, 0, 0));
+
+	// Count frequencies, but only for every 8th block or so, randomly selected.
+	uint wg_index = gl_WorkGroupID.y * gl_WorkGroupSize.x + gl_WorkGroupID.x;
+	if ((wg_index * 0x9E3779B9u) >> 29 == 0) {  // Fibonacci hashing, essentially a PRNG in this context.
+		c0 = min(abs(c0), 255);
+		c1 = min(abs(c1), 255);
+		c2 = min(abs(c2), 255);
+		c3 = min(abs(c3), 255);
+		c4 = min(abs(c4), 255);
+		c5 = min(abs(c5), 255);
+		c6 = min(abs(c6), 255);
+		c7 = min(abs(c7), 255);
+
+		// Spread out the most popular elements among the cache lines by reversing the bits
+		// of the index, reducing false sharing.
+		c0 = bitfieldReverse(c0) >> 24;
+		c1 = bitfieldReverse(c1) >> 24;
+		c2 = bitfieldReverse(c2) >> 24;
+		c3 = bitfieldReverse(c3) >> 24;
+		c4 = bitfieldReverse(c4) >> 24;
+		c5 = bitfieldReverse(c5) >> 24;
+		c6 = bitfieldReverse(c6) >> 24;
+		c7 = bitfieldReverse(c7) >> 24;
+
+		uint m = luma_mapping[n];
+		atomicAdd(dist[bitfieldExtract(m,  0, 2)][c0], 1);
+		atomicAdd(dist[bitfieldExtract(m,  2, 2)][c1], 1);
+		atomicAdd(dist[bitfieldExtract(m,  4, 2)][c2], 1);
+		atomicAdd(dist[bitfieldExtract(m,  6, 2)][c3], 1);
+		atomicAdd(dist[bitfieldExtract(m,  8, 2)][c4], 1);
+		atomicAdd(dist[bitfieldExtract(m, 10, 2)][c5], 1);
+		atomicAdd(dist[bitfieldExtract(m, 12, 2)][c6], 1);
+		atomicAdd(dist[bitfieldExtract(m, 14, 2)][c7], 1);
+	}
 }
 
diff --git a/narabu-encoder.cpp b/narabu-encoder.cpp
index 2ddd899..e8d20e0 100644
--- a/narabu-encoder.cpp
+++ b/narabu-encoder.cpp
@@ -334,6 +334,13 @@ int main(int argc, char **argv)
 
 	glUseProgram(glsl_program_num);
 
+	// An SSBO for the rANS distributions.
+	GLuint ssbo;
+	glGenBuffers(1, &ssbo);
+	glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
+	glBufferData(GL_SHADER_STORAGE_BUFFER, 65536 * 4 * sizeof(uint32_t), nullptr, GL_DYNAMIC_COPY);
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 9, ssbo);
+
 	// Upload luma.
 	GLuint y_tex;
 	glGenTextures(1, &y_tex);
@@ -392,7 +399,7 @@ int main(int argc, char **argv)
 	check_error();
 
 	steady_clock::time_point start = steady_clock::now();
-	unsigned num_iterations = 1000;
+	unsigned num_iterations = 100;
 	for (unsigned i = 0; i < num_iterations; ++i) {
 		glDispatchCompute(WIDTH_BLOCKS, HEIGHT_BLOCKS, 1);
 	}
@@ -575,4 +582,11 @@ int main(int argc, char **argv)
 	printf("\n");
 	printf("Each iteration took %.3f ms (but note that is DCT only, no rANS).\n", 1e3 * duration<double>(now - start).count() / num_iterations);
 
+#if 1
+	glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
+	const uint32_t *dist = (const uint32_t *)glMapBuffer(GL_SHADER_STORAGE_BUFFER, GL_READ_ONLY);
+	for (int i = 0; i < 1024; ++i) {
+		printf("%d,%d: %u\n", i / 256, i % 256, dist[i] / num_iterations);
+	}
+#endif
 }