From fedc6308264085999789854152c9577ddfe1bc6e Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Tue, 17 Oct 2017 23:28:25 +0200
Subject: [PATCH] Encapsulate things a bit better in rans.shader.

---
 rans.shader | 48 ++++++++++++++++++++++++++----------------------
 1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/rans.shader b/rans.shader
index 965c674..39efc52 100644
--- a/rans.shader
+++ b/rans.shader
@@ -54,6 +54,11 @@ layout(r16ui) uniform restrict readonly uimage2D ac2_ac5_tex;
 layout(r8i) uniform restrict readonly iimage2D ac3_tex;
 layout(r8i) uniform restrict readonly iimage2D ac4_tex;
 
+void RansPutByte(uint x, inout RansEncoder enc)
+{
+	rans_output[--enc.rans_offset] = uint8_t(x);
+}
+
 void RansEncInit(uint streamgroup_num, uint coeff_row, uint coeff_col, uint dist_num, out RansEncoder enc)
 {
 	enc.stream_num = streamgroup_num * 64 + coeff_row * 8 + coeff_col;
@@ -63,22 +68,22 @@ void RansEncInit(uint streamgroup_num, uint coeff_row, uint coeff_col, uint dist
 	enc.rans = RANS_BYTE_L;
 }
 
-void RansEncRenorm(inout uint rans, inout uint rans_offset, uint freq, uint prob_bits)
+void RansEncRenorm(inout RansEncoder enc, uint freq, uint prob_bits)
 {
 	uint x_max = ((RANS_BYTE_L >> prob_bits) << 8) * freq; // this turns into a shift.
-	while (rans >= x_max) {
-		rans_output[--rans_offset] = uint8_t(rans & 0xffu);
-		rans >>= 8;
+	while (enc.rans >= x_max) {
+		RansPutByte(enc.rans & 0xffu, enc);
+		enc.rans >>= 8;
 	}
 }
 
-void RansEncPut(inout uint rans, inout uint rans_offset, uint start, uint freq, uint prob_bits)
+void RansEncPut(inout RansEncoder enc, uint start, uint freq, uint prob_bits)
 {
-	RansEncRenorm(rans, rans_offset, freq, prob_bits);
-	rans = ((rans / freq) << prob_bits) + (rans % freq) + start;
+	RansEncRenorm(enc, freq, prob_bits);
+	enc.rans = ((enc.rans / freq) << prob_bits) + (enc.rans % freq) + start;
 }
 
-void RansEncPutSymbol(inout uint rans, inout uint rans_offset, uvec4 sym)
+void RansEncPutSymbol(inout RansEncoder enc, uvec4 sym)
 {
 	uint x_max = sym.x;
 	uint rcp_freq = sym.y;
@@ -87,23 +92,22 @@ void RansEncPutSymbol(inout uint rans, inout uint rans_offset, uvec4 sym)
 	uint cmpl_freq = (sym.w >> 16);
 
 	// renormalize
-	while (rans >= x_max) {
-		rans_output[--rans_offset] = uint8_t(rans & 0xffu);
-		rans >>= 8;
+	while (enc.rans >= x_max) {
+		RansPutByte(enc.rans & 0xffu, enc);
+		enc.rans >>= 8;
 	}
 
 	uint q, unused;
-	umulExtended(rans, rcp_freq, q, unused);
-	rans += bias + (q >> rcp_shift) * cmpl_freq;
+	umulExtended(enc.rans, rcp_freq, q, unused);
+	enc.rans += bias + (q >> rcp_shift) * cmpl_freq;
 }
 
-void RansEncFlush(uint rans, inout uint rans_offset)
+void RansEncFlush(inout RansEncoder enc)
 {
-	rans_offset -= 4;
-	rans_output[rans_offset + 0] = uint8_t(rans >> 0);
-	rans_output[rans_offset + 1] = uint8_t(rans >> 8);
-	rans_output[rans_offset + 2] = uint8_t(rans >> 16);
-	rans_output[rans_offset + 3] = uint8_t(rans >> 24);
+	RansPutByte(enc.rans >> 24, enc);
+	RansPutByte(enc.rans >> 16, enc);
+	RansPutByte(enc.rans >> 8, enc);
+	RansPutByte(enc.rans >> 0, enc);
 }
 
 int sign_extend(uint coeff, uint bits)
@@ -119,12 +123,12 @@ void encode_coeff(int signed_k, inout RansEncoder enc)
 		// 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);
+		RansEncPut(enc, k, 1, prob_bits);
 		k = ESCAPE_LIMIT;
 	}
 
 	uvec4 sym = ransdist[enc.lut_base + ((k - 1) & (NUM_SYMS - 1))];
-	RansEncPutSymbol(enc.rans, enc.rans_offset, sym);
+	RansEncPutSymbol(enc, sym);
 	
 	if (signed_k < 0) {
 		enc.rans += enc.sign_bias;
@@ -133,7 +137,7 @@ void encode_coeff(int signed_k, inout RansEncoder enc)
 
 void encode_end(inout RansEncoder enc)
 {
-	RansEncFlush(enc.rans, enc.rans_offset);
+	RansEncFlush(enc);
 	rans_start_offset[enc.stream_num] = enc.rans_offset;
 }
 
-- 
2.39.2