Align with KDFS 1.4.0 rounding update

Docs/ChangeLog-5x.md

@@ -18,6 +18,10 @@ header.  We always recommend rebuilding your client-side code using the
 header from the same release to avoid compatibility issues.
 
 * **General:**
+  * **Change:** Changed sRGB alpha channel endpoint expansion to match the
+    revised Khronos Data Format Specification (v1.4.0), which reverts an
+    unintended specification change. Compared to previous releases, this change
+    can cause LSB bit differences in the alpha channel of compressed images.
   * **Feature:** Arm64 builds for Linux added to the GitHub Actions builds, and
     Arm64 binaries for NEON, 128-bit SVE 128 and 256-bit SVE added to release
     builds.

Source/astcenc_color_unquantize.cpp

@@ -925,15 +925,8 @@ void unpack_color_endpoints(
 			alpha_hdr = false;
 		}
 
-		vmask4 mask(true, true, true, false);
-
-		vint4 output0rgb = lsl<8>(output0) | vint4(0x80);
-		vint4 output0a = output0 * 257;
-		output0 = select(output0a, output0rgb, mask);
-
-		vint4 output1rgb = lsl<8>(output1) | vint4(0x80);
-		vint4 output1a = output1 * 257;
-		output1 = select(output1a, output1rgb, mask);
+		output0 = lsl<8>(output0) | vint4(0x80);
+		output1 = lsl<8>(output1) | vint4(0x80);
 	}
 	// An HDR profile decode, but may be using linear LDR endpoints
 	// Linear LDR 8-bit endpoints are expanded to 16-bit by replication

Source/astcenc_internal.h

@@ -1583,19 +1583,13 @@ static inline vmask4 get_u8_component_mask(
 	astcenc_profile decode_mode,
 	const image_block& blk
 ) {
-	vmask4 u8_mask(false);
-	// Decode mode writing to a unorm8 output value
-	if (blk.decode_unorm8)
+	// Decode mode or sRGB forces writing to unorm8 output value
+	if (blk.decode_unorm8 || decode_mode == ASTCENC_PRF_LDR_SRGB)
 	{
-		u8_mask = vmask4(true);
-	}
-	// SRGB writing to a unorm8 RGB value
-	else if (decode_mode == ASTCENC_PRF_LDR_SRGB)
-	{
-		u8_mask = vmask4(true, true, true, false);
+		return vmask4(true);
 	}
 
-	return u8_mask;
+	return vmask4(false);
 }
 
 /**

Test/astc_test_image.py

@@ -319,7 +319,7 @@ def parse_command_line():
     parser.add_argument("--encoder", dest="encoders", default="avx2",
                         choices=coders, help="test encoder variant")
 
-    parser.add_argument("--reference", dest="reference", default="ref-5.0-avx2",
+    parser.add_argument("--reference", dest="reference", default="ref-main-avx2",
                         choices=refcoders, help="reference encoder variant")
 
     astcProfile = ["ldr", "ldrs", "hdr", "all"]