X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=rans.shader;h=c0272312118a4a00a00a9c0ce6197fb8616691dc;hb=88ff4031f4d927b95106b8462ec4bd3c9edef718;hp=b77d2407adab28496e783a1953d76f043f312b51;hpb=b877c1eae5d301a3ce36e0ba9b0b830a95e06ec8;p=narabu

diff --git a/rans.shader b/rans.shader
index b77d240..c027231 100644
--- a/rans.shader
+++ b/rans.shader
@@ -3,7 +3,7 @@
 
 layout(local_size_x = 1) in;
 
-const uint prob_bits = 13;  // Note!
+const uint prob_bits = 12;
 const uint prob_scale = 1 << prob_bits;
 const uint RANS_BYTE_L = (1u << 23);
 const uint BLOCKS_PER_STREAM = 320;
@@ -24,12 +24,6 @@ const uint luma_mapping[8] = {
 	MAPPING(3, 3, 3, 3, 3, 3, 3, 3),
 };
 
-layout(std430, binding = 9) buffer layoutName
-{
-	uint dist[4 * 256];
-	uvec2 ransdist[4 * 256];
-};
-
 layout(std430, binding = 10) buffer outputBuf
 {
 	uint8_t rans_output[];
@@ -40,9 +34,16 @@ layout(std430, binding = 11) buffer outputBuf2
 	uint rans_start_offset[];
 };
 
+layout(std140, binding = 13) uniform DistBlock
+{
+	uvec4 ransdist[4 * 256];
+	uint sign_biases[4];
+};
+
 struct RansEncoder {
 	uint stream_num;   // const
 	uint lut_base;     // const
+	uint sign_bias;    // const
 	uint rans_offset;
 	uint rans;
 };
@@ -57,6 +58,7 @@ void RansEncInit(uint streamgroup_num, uint coeff_row, uint coeff_col, uint dist
 {
 	enc.stream_num = streamgroup_num * 64 + coeff_row * 8 + coeff_col;
 	enc.lut_base = dist_num * 256;
+	enc.sign_bias = sign_biases[dist_num];
 	enc.rans_offset = enc.stream_num * STREAM_BUF_SIZE + STREAM_BUF_SIZE;  // Starts at the end.
 	enc.rans = RANS_BYTE_L;
 }
@@ -64,11 +66,9 @@ void RansEncInit(uint streamgroup_num, uint coeff_row, uint coeff_col, uint dist
 void RansEncRenorm(inout uint rans, inout uint rans_offset, uint freq, uint prob_bits)
 {
 	uint x_max = ((RANS_BYTE_L >> prob_bits) << 8) * freq; // this turns into a shift.
-	if (rans >= x_max) {
-		do {
-			rans_output[--rans_offset] = uint8_t(rans & 0xff);
-			rans >>= 8;
-		} while (rans >= x_max);
+	while (rans >= x_max) {
+		rans_output[--rans_offset] = uint8_t(rans & 0xffu);
+		rans >>= 8;
 	}
 }
 
@@ -78,6 +78,27 @@ void RansEncPut(inout uint rans, inout uint rans_offset, uint start, uint freq,
 	rans = ((rans / freq) << prob_bits) + (rans % freq) + start;
 }
 
+void RansEncPutSymbol(inout uint rans, inout uint rans_offset, uvec4 sym)
+{
+	uint x_max = sym.x;
+	uint rcp_freq = sym.y;
+	uint bias = sym.z;
+	uint rcp_shift = (sym.w & 0xffffu);
+	uint cmpl_freq = (sym.w >> 16);
+
+	// renormalize
+	if (rans >= x_max) {
+		do {
+			rans_output[--rans_offset] = uint8_t(rans & 0xffu);
+			rans >>= 8;
+		} while (rans >= x_max);
+	}
+
+	uint q, unused;
+	umulExtended(rans, rcp_freq, q, unused);
+	rans += bias + (q >> rcp_shift) * cmpl_freq;
+}
+
 void RansEncFlush(uint rans, inout uint rans_offset)
 {
 	rans_offset -= 4;
@@ -92,21 +113,23 @@ int sign_extend(uint coeff, uint bits)
 	return int(coeff << (32 - bits)) >> (32 - bits);
 }
 
-void encode_coeff(int signed_k, uint sign_bias, inout RansEncoder enc)
+void encode_coeff(int signed_k, inout RansEncoder enc)
 {
 	uint k = abs(signed_k);
 
 	if (k >= ESCAPE_LIMIT) {
-		// ... boring stuff here
-		RansEncPut(enc.rans, enc.rans_offset, k, 1, prob_bits - 1);
+		// Put the coefficient as a 1/(2^12) symbol _before_
+		// the 255 coefficient, since the decoder will read the
+		// 255 coefficient first.
+		RansEncPut(enc.rans, enc.rans_offset, k, 1, prob_bits);
 		k = ESCAPE_LIMIT;
 	}
 
-	uvec2 sym = ransdist[enc.lut_base + (k + NUM_SYMS - 1) & (NUM_SYMS - 1)];
-	RansEncPut(enc.rans, enc.rans_offset, sym.x, sym.y, prob_bits);
+	uvec4 sym = ransdist[enc.lut_base + ((k - 1) & (NUM_SYMS - 1))];
+	RansEncPutSymbol(enc.rans, enc.rans_offset, sym);
 	
 	if (signed_k < 0) {
-		enc.rans += sign_bias;
+		enc.rans += enc.sign_bias;
 	}
 }
 
@@ -122,17 +145,14 @@ void encode_9_7(uint streamgroup_num, uint coeff_row, layout(r16ui) restrict rea
 	RansEncInit(streamgroup_num, coeff_row, col1, dist1, enc1);
 	RansEncInit(streamgroup_num, coeff_row, col2, dist2, enc2);
 
-	uint sign_bias1 = ransdist[enc1.lut_base + 255].x + ransdist[enc1.lut_base + 255].y;
-	uint sign_bias2 = ransdist[enc2.lut_base + 255].x + ransdist[enc2.lut_base + 255].y;
-
-	for (uint subblock_idx = BLOCKS_PER_STREAM; subblock_idx --> 0; ) {
+	for (uint subblock_idx = 0; subblock_idx < BLOCKS_PER_STREAM; ++subblock_idx) {
 		// TODO: Use SSBOs instead of a texture?
 		uint x = (streamgroup_num * BLOCKS_PER_STREAM + subblock_idx) % 160;
 		uint y = (streamgroup_num * BLOCKS_PER_STREAM + subblock_idx) / 160;
 		uint f = imageLoad(tex, ivec2(x, y * 8 + coeff_row)).x;
 
-		encode_coeff(sign_extend(f & 0x1ffu, 9), sign_bias1, enc1);
-		encode_coeff(sign_extend(f >> 9, 7), sign_bias2, enc2);
+		encode_coeff(sign_extend(f & 0x1ffu, 9), enc1);
+		encode_coeff(sign_extend(f >> 9, 7), enc2);
 	}
 
 	encode_end(enc1);
@@ -144,15 +164,13 @@ void encode_8(uint streamgroup_num, uint coeff_row, layout(r8i) restrict readonl
 	RansEncoder enc;
 	RansEncInit(streamgroup_num, coeff_row, col, dist, enc);
 
-	uint sign_bias = ransdist[enc.lut_base + 255].x + ransdist[enc.lut_base + 255].y;
-
-	for (uint subblock_idx = BLOCKS_PER_STREAM; subblock_idx --> 0; ) {
+	for (uint subblock_idx = 0; subblock_idx < BLOCKS_PER_STREAM; ++subblock_idx) {
 		// TODO: Use SSBOs instead of a texture?
 		uint x = (streamgroup_num * BLOCKS_PER_STREAM + subblock_idx) % 160;
 		uint y = (streamgroup_num * BLOCKS_PER_STREAM + subblock_idx) / 160;
 		int f = imageLoad(tex, ivec2(x, y * 8 + coeff_row)).x;
 
-		encode_coeff(f, sign_bias, enc);
+		encode_coeff(f, enc);
 	}
 
 	encode_end(enc);