i965: Add functions to convert float <-> VF.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/Makefile.sources

@@ -79,6 +79,7 @@ i965_FILES = \
 	brw_meta_fast_clear.c \
 	brw_misc_state.c \
 	brw_object_purgeable.c \
+	brw_packed_float.c \
 	brw_performance_monitor.c \
 	brw_program.c \
 	brw_primitive_restart.c \

src/mesa/drivers/dri/i965/brw_packed_float.c

@@ -0,0 +1,75 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * 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.
+ */
+#include "brw_reg.h"
+
+union fu {
+   float f;
+   unsigned u;
+   struct {
+      unsigned mantissa:23;
+      unsigned exponent:8;
+      unsigned sign:1;
+   };
+};
+
+int
+brw_float_to_vf(float f)
+{
+   union fu fu = { .f = f };
+
+   /* ±0.0f is special cased. */
+   if (f == 0.0f)
+      return fu.sign << 7;
+
+   unsigned mantissa = fu.mantissa >> (23 - 4);
+   unsigned exponent = fu.exponent - (127 - 3);
+   unsigned vf = (fu.sign << 7) | (exponent << 4) | mantissa;
+
+   /* 0.125 would have had the same representation as 0.0, so reject it. */
+   if ((vf & 0x7f) == 0)
+      return -1;
+
+   /* Make sure the mantissa fits in 4-bits and the exponent in 3-bits. */
+   if (fu.u & 0x7ffff || exponent > 7)
+      return -1;
+
+   return vf;
+}
+
+float
+brw_vf_to_float(unsigned char vf)
+{
+   union fu fu;
+
+   /* ±0.0f is special cased. */
+   if (vf == 0x00 || vf == 0x80) {
+      fu.u = vf << 24;
+      return fu.f;
+   }
+
+   fu.sign = vf >> 7;
+   fu.exponent = ((vf & 0x70) >> 4) + (127 - 3);
+   fu.mantissa = (vf & 0xf) << (23 - 4);
+
+   return fu.f;
+}

src/mesa/drivers/dri/i965/brw_reg.h

@@ -881,6 +881,10 @@ brw_indirect(unsigned addr_subnr, int offset)
    return ptr;
 }
 
+/* brw_packed_float.c */
+int brw_float_to_vf(float f);
+float brw_vf_to_float(unsigned char vf);
+
 #ifdef __cplusplus
 }
 #endif