libobs: Add basic support for half floats

libobs/CMakeLists.txt

@@ -289,6 +289,7 @@ set(libobs_graphics_SOURCES
 	graphics/math-extra.c
 	graphics/graphics-imports.c)
 set(libobs_graphics_HEADERS
+	graphics/half.h
 	graphics/plane.h
 	graphics/quat.h
 	graphics/input.h

libobs/graphics/half.h

@@ -0,0 +1,102 @@
+/******************************************************************************
+    Copyright (C) 2020 by Hugh Bailey <[email protected]>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+******************************************************************************/
+
+/******************************************************************************
+                               The MIT License (MIT)
+
+Copyright (c) 2011-2019 Microsoft Corp
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this 
+software and associated documentation files (the "Software"), to deal in the Software 
+without restriction, including without limitation the rights to use, copy, modify, 
+merge, publish, distribute, sublicense, and/or sell copies of the Software, and to 
+permit persons to whom the Software is furnished to do so, subject to the following 
+conditions: 
+
+The above copyright notice and this permission notice shall be included in all copies 
+or substantial portions of the Software.  
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, 
+INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A 
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF 
+CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE 
+OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+******************************************************************************/
+
+#pragma once
+
+#include "math-defs.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct half {
+	uint16_t u;
+};
+
+/* adapted from DirectXMath XMConvertFloatToHalf */
+inline struct half half_from_float(float f)
+{
+	uint32_t Result;
+
+	uint32_t IValue;
+	memcpy(&IValue, &f, sizeof(IValue));
+	uint32_t Sign = (IValue & 0x80000000U) >> 16U;
+	IValue = IValue & 0x7FFFFFFFU; // Hack off the sign
+
+	if (IValue > 0x477FE000U) {
+		// The number is too large to be represented as a half.  Saturate to infinity.
+		if (((IValue & 0x7F800000) == 0x7F800000) &&
+		    ((IValue & 0x7FFFFF) != 0)) {
+			Result = 0x7FFF; // NAN
+		} else {
+			Result = 0x7C00U; // INF
+		}
+	} else if (!IValue) {
+		Result = 0;
+	} else {
+		if (IValue < 0x38800000U) {
+			// The number is too small to be represented as a normalized half.
+			// Convert it to a denormalized value.
+			uint32_t Shift = 113U - (IValue >> 23U);
+			IValue = (0x800000U | (IValue & 0x7FFFFFU)) >> Shift;
+		} else {
+			// Rebias the exponent to represent the value as a normalized half.
+			IValue += 0xC8000000U;
+		}
+
+		Result = ((IValue + 0x0FFFU + ((IValue >> 13U) & 1U)) >> 13U) &
+			 0x7FFFU;
+	}
+
+	struct half h;
+	h.u = (uint16_t)(Result | Sign);
+	return h;
+}
+
+inline struct half half_from_bits(uint16_t u)
+{
+	struct half h;
+	h.u = u;
+	return h;
+}
+
+#ifdef __cplusplus
+}
+#endif