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src/util/format_rgb9e5.h

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+/*
+ * Copyright (C) 2011 Marek Olšák <[email protected]>
+ *
+ * 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 (including the next
+ * paragraph) 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.
+ */
+
+/* Copied from EXT_texture_shared_exponent and edited, getting rid of
+ * expensive float math bits too. */
+
+#ifndef RGB9E5_H
+#define RGB9E5_H
+
+#include <assert.h>
+#include <stdint.h>
+#include <math.h>
+
+#define RGB9E5_EXPONENT_BITS          5
+#define RGB9E5_MANTISSA_BITS          9
+#define RGB9E5_EXP_BIAS               15
+#define RGB9E5_MAX_VALID_BIASED_EXP   31
+
+#define MAX_RGB9E5_EXP               (RGB9E5_MAX_VALID_BIASED_EXP - RGB9E5_EXP_BIAS)
+#define RGB9E5_MANTISSA_VALUES       (1<<RGB9E5_MANTISSA_BITS)
+#define MAX_RGB9E5_MANTISSA          (RGB9E5_MANTISSA_VALUES-1)
+#define MAX_RGB9E5                   (((float)MAX_RGB9E5_MANTISSA)/RGB9E5_MANTISSA_VALUES * (1<<MAX_RGB9E5_EXP))
+
+static inline int rgb9e5_ClampRange(float x)
+{
+   union { float f; uint32_t u; } f, max;
+   f.f = x;
+   max.f = MAX_RGB9E5;
+
+   if (f.u > 0x7f800000)
+  /* catches neg, NaNs */
+      return 0;
+   else if (f.u >= max.u)
+      return max.u;
+   else
+      return f.u;
+}
+
+static inline uint32_t float3_to_rgb9e5(const float rgb[3])
+{
+   int rm, gm, bm;
+   uint32_t exp_shared;
+   uint32_t revdenom_biasedexp;
+   union { float f; uint32_t u; } rc, bc, gc, maxrgb, revdenom;
+
+   rc.u = rgb9e5_ClampRange(rgb[0]);
+   gc.u = rgb9e5_ClampRange(rgb[1]);
+   bc.u = rgb9e5_ClampRange(rgb[2]);
+   maxrgb.u = MAX3(rc.u, gc.u, bc.u);
+
+   /*
+    * Compared to what the spec suggests, instead of conditionally adjusting
+    * the exponent after the fact do it here by doing the equivalent of +0.5 -
+    * the int add will spill over into the exponent in this case.
+    */
+   maxrgb.u += maxrgb.u & (1 << (23-9));
+   exp_shared = MAX2((maxrgb.u >> 23), -RGB9E5_EXP_BIAS - 1 + 127) +
+                1 + RGB9E5_EXP_BIAS - 127;
+   revdenom_biasedexp = 127 - (exp_shared - RGB9E5_EXP_BIAS -
+                               RGB9E5_MANTISSA_BITS) + 1;
+   revdenom.u = revdenom_biasedexp << 23;
+   assert(exp_shared <= RGB9E5_MAX_VALID_BIASED_EXP);
+
+   /*
+    * The spec uses strict round-up behavior (d3d10 disagrees, but in any case
+    * must match what is done above for figuring out exponent).
+    * We avoid the doubles ((int) rc * revdenom + 0.5) by doing the rounding
+    * ourselves (revdenom was adjusted by +1, above).
+    */
+   rm = (int) (rc.f * revdenom.f);
+   gm = (int) (gc.f * revdenom.f);
+   bm = (int) (bc.f * revdenom.f);
+   rm = (rm & 1) + (rm >> 1);
+   gm = (gm & 1) + (gm >> 1);
+   bm = (bm & 1) + (bm >> 1);
+
+   assert(rm <= MAX_RGB9E5_MANTISSA);
+   assert(gm <= MAX_RGB9E5_MANTISSA);
+   assert(bm <= MAX_RGB9E5_MANTISSA);
+   assert(rm >= 0);
+   assert(gm >= 0);
+   assert(bm >= 0);
+
+   return (exp_shared << 27) | (bm << 18) | (gm << 9) | rm;
+}
+
+static inline void rgb9e5_to_float3(uint32_t rgb, float retval[3])
+{
+   int exponent;
+   union { float f; uint32_t u; } scale;
+
+   exponent = (rgb >> 27) - RGB9E5_EXP_BIAS - RGB9E5_MANTISSA_BITS;
+   scale.u = (exponent + 127) << 23;
+
+   retval[0] = ( rgb        & 0x1ff) * scale.f;
+   retval[1] = ((rgb >> 9)  & 0x1ff) * scale.f;
+   retval[2] = ((rgb >> 18) & 0x1ff) * scale.f;
+}
+
+#endif