2 * Copyright (C) 2011 Marek Olšák <maraeo@gmail.com>
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
21 * DEALINGS IN THE SOFTWARE.
24 /* Copied from EXT_texture_shared_exponent and edited, getting rid of
25 * expensive float math bits too. */
35 #define RGB9E5_EXPONENT_BITS 5
36 #define RGB9E5_MANTISSA_BITS 9
37 #define RGB9E5_EXP_BIAS 15
38 #define RGB9E5_MAX_VALID_BIASED_EXP 31
40 #define MAX_RGB9E5_EXP (RGB9E5_MAX_VALID_BIASED_EXP - RGB9E5_EXP_BIAS)
41 #define RGB9E5_MANTISSA_VALUES (1<<RGB9E5_MANTISSA_BITS)
42 #define MAX_RGB9E5_MANTISSA (RGB9E5_MANTISSA_VALUES-1)
43 #define MAX_RGB9E5 (((float)MAX_RGB9E5_MANTISSA)/RGB9E5_MANTISSA_VALUES * (1<<MAX_RGB9E5_EXP))
45 static inline int rgb9e5_ClampRange(float x
)
47 union { float f
; uint32_t u
; } f
, max
;
52 /* catches neg, NaNs */
54 else if (f
.u
>= max
.u
)
60 static inline uint32_t float3_to_rgb9e5(const float rgb
[3])
62 int rm
, gm
, bm
, exp_shared
;
63 uint32_t revdenom_biasedexp
;
64 union { float f
; uint32_t u
; } rc
, bc
, gc
, maxrgb
, revdenom
;
66 rc
.u
= rgb9e5_ClampRange(rgb
[0]);
67 gc
.u
= rgb9e5_ClampRange(rgb
[1]);
68 bc
.u
= rgb9e5_ClampRange(rgb
[2]);
69 maxrgb
.u
= MAX3(rc
.u
, gc
.u
, bc
.u
);
72 * Compared to what the spec suggests, instead of conditionally adjusting
73 * the exponent after the fact do it here by doing the equivalent of +0.5 -
74 * the int add will spill over into the exponent in this case.
76 maxrgb
.u
+= maxrgb
.u
& (1 << (23-9));
77 exp_shared
= MAX2((maxrgb
.u
>> 23), -RGB9E5_EXP_BIAS
- 1 + 127) +
78 1 + RGB9E5_EXP_BIAS
- 127;
79 revdenom_biasedexp
= 127 - (exp_shared
- RGB9E5_EXP_BIAS
-
80 RGB9E5_MANTISSA_BITS
) + 1;
81 revdenom
.u
= revdenom_biasedexp
<< 23;
82 assert(exp_shared
<= RGB9E5_MAX_VALID_BIASED_EXP
);
85 * The spec uses strict round-up behavior (d3d10 disagrees, but in any case
86 * must match what is done above for figuring out exponent).
87 * We avoid the doubles ((int) rc * revdenom + 0.5) by doing the rounding
88 * ourselves (revdenom was adjusted by +1, above).
90 rm
= (int) (rc
.f
* revdenom
.f
);
91 gm
= (int) (gc
.f
* revdenom
.f
);
92 bm
= (int) (bc
.f
* revdenom
.f
);
93 rm
= (rm
& 1) + (rm
>> 1);
94 gm
= (gm
& 1) + (gm
>> 1);
95 bm
= (bm
& 1) + (bm
>> 1);
97 assert(rm
<= MAX_RGB9E5_MANTISSA
);
98 assert(gm
<= MAX_RGB9E5_MANTISSA
);
99 assert(bm
<= MAX_RGB9E5_MANTISSA
);
104 return (exp_shared
<< 27) | (bm
<< 18) | (gm
<< 9) | rm
;
107 static inline void rgb9e5_to_float3(uint32_t rgb
, float retval
[3])
110 union { float f
; uint32_t u
; } scale
;
112 exponent
= (rgb
>> 27) - RGB9E5_EXP_BIAS
- RGB9E5_MANTISSA_BITS
;
113 scale
.u
= (exponent
+ 127) << 23;
115 retval
[0] = ( rgb
& 0x1ff) * scale
.f
;
116 retval
[1] = ((rgb
>> 9) & 0x1ff) * scale
.f
;
117 retval
[2] = ((rgb
>> 18) & 0x1ff) * scale
.f
;