From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Mon, 16 Oct 2017 20:30:57 +0000 (+0200)
Subject: Save some needless sign extending, and fix an escaping bug.
X-Git-Url: https://git.sesse.net/?p=narabu;a=commitdiff_plain;h=b877c1eae5d301a3ce36e0ba9b0b830a95e06ec8;ds=sidebyside

Save some needless sign extending, and fix an escaping bug.
---

diff --git a/coded.dat b/coded.dat
index 3980407..bfe60fb 100644
Binary files a/coded.dat and b/coded.dat differ
diff --git a/rans.shader b/rans.shader
index 36feb65..b77d240 100644
--- a/rans.shader
+++ b/rans.shader
@@ -87,16 +87,18 @@ void RansEncFlush(uint rans, inout uint rans_offset)
 	rans_output[rans_offset + 3] = uint8_t(rans >> 24);
 }
 
-void encode_coeff(uint coeff, uint bits, uint sign_bias, inout RansEncoder enc)
+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)
 {
-	// Sign-extend to recover the coefficient.
-	// FIXME: not needed for the bits == 8 case!
-	int signed_k = int(coeff << (32 - bits)) >> (32 - bits);
 	uint k = abs(signed_k);
 
 	if (k >= ESCAPE_LIMIT) {
 		// ... boring stuff here
-		RansEncPut(enc.rans, enc.rans_offset, k, 1, prob_bits);
+		RansEncPut(enc.rans, enc.rans_offset, k, 1, prob_bits - 1);
 		k = ESCAPE_LIMIT;
 	}
 
@@ -129,8 +131,8 @@ void encode_9_7(uint streamgroup_num, uint coeff_row, layout(r16ui) restrict rea
 		uint y = (streamgroup_num * BLOCKS_PER_STREAM + subblock_idx) / 160;
 		uint f = imageLoad(tex, ivec2(x, y * 8 + coeff_row)).x;
 
-		encode_coeff(f & 0x1ffu, 9, sign_bias1, enc1);
-		encode_coeff(f >> 9, 7, sign_bias2, enc2);
+		encode_coeff(sign_extend(f & 0x1ffu, 9), sign_bias1, enc1);
+		encode_coeff(sign_extend(f >> 9, 7), sign_bias2, enc2);
 	}
 
 	encode_end(enc1);
@@ -150,7 +152,7 @@ void encode_8(uint streamgroup_num, uint coeff_row, layout(r8i) restrict readonl
 		uint y = (streamgroup_num * BLOCKS_PER_STREAM + subblock_idx) / 160;
 		int f = imageLoad(tex, ivec2(x, y * 8 + coeff_row)).x;
 
-		encode_coeff(f, 8, sign_bias, enc);
+		encode_coeff(f, sign_bias, enc);
 	}
 
 	encode_end(enc);