3 files changed, 195 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_gctors.cpp b/src/gallium/auxiliary/util/u_gctors.cpp
new file mode 100644
index 0000000000..9ea9819d73
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_gctors.cpp
@@ -0,0 +1,17 @@
+/* this file uses the C++ global constructor mechanism to automatically
+   initialize global data
+
+   __attribute__((constructor)) allows to do this in C, but is GCC-only
+*/
+
+extern "C" void util_half_init_tables(void);
+
+struct util_gctor_t
+{
+	util_gctor_t()
+	{
+		util_half_init_tables();
+	}
+};
+
+static struct util_gctor_t util_gctor;
diff --git a/src/gallium/auxiliary/util/u_half.c b/src/gallium/auxiliary/util/u_half.c
new file mode 100644
index 0000000000..8865acb76b
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_half.c
@@ -0,0 +1,123 @@
+#include "util/u_half.h"
+
+/* see www.fox-toolkit.org/ftp/fasthalffloatconversion.pdf
+ * "Fast Half Float Conversions" by Jeroen van der Zijp, Nov 2008
+ */
+
+/* Note that using a 64K * 4 table is a terrible idea since it will not fit
+ * in the L1 cache and will massively pollute the L2 cache as well
+ *
+ * These should instead fit in the L1 cache.
+ *
+ * TODO: we could use a denormal bias table instead of the mantissa/offset
+ * tables: this would reduce the L1 cache usage from 8704 to 2304 bytes
+ * but would involve more computation
+ *
+ * Note however that if denormals are never encountered, the L1 cache usage
+ * is only about 4608 bytes anyway.
+ */
+uint32_t util_half_to_float_mantissa_table[2048];
+uint32_t util_half_to_float_exponent_table[64];
+uint32_t util_half_to_float_offset_table[64];
+uint16_t util_float_to_half_base_table[512];
+uint8_t util_float_to_half_shift_table[512];
+
+/* called by u_gctors.cpp, which defines the prototype itself */
+void util_half_init_tables(void);
+
+void util_half_init_tables(void)
+{
+	int i;
+
+	/* zero */
+	util_half_to_float_mantissa_table[0] = 0;
+
+	/* denormals */
+	for(i = 1; i < 1024; ++i) {
+		unsigned int m = i << 13;
+		unsigned int e = 0;
+
+		/* Normalize number */
+		while(!(m & 0x00800000)) {
+			e -= 0x00800000;
+			m<<=1;
+		}
+		m &= ~0x00800000;
+		e+= 0x38800000;
+		util_half_to_float_mantissa_table[i] = m | e;
+	}
+
+	/* normals */
+	for(i = 1024; i < 2048; ++i)
+		util_half_to_float_mantissa_table[i] = ((i-1024)<<13);
+
+	/* positive zero or denormals */
+	util_half_to_float_exponent_table[0] = 0;
+
+	/* positive numbers */
+	for(i = 1; i <= 30; ++i)
+		util_half_to_float_exponent_table[i] = 0x38000000 + (i << 23);
+
+	/* positive infinity/NaN */
+	util_half_to_float_exponent_table[31] = 0x7f800000;
+
+	/* negative zero or denormals */
+	util_half_to_float_exponent_table[32] = 0x80000000;
+
+	/* negative numbers */
+	for(i = 33; i <= 62; ++i)
+		util_half_to_float_exponent_table[i] = 0xb8000000 + ((i - 32) << 23);
+
+	/* negative infinity/NaN */
+	util_half_to_float_exponent_table[63] = 0xff800000;
+
+	/* positive zero or denormals */
+	util_half_to_float_offset_table[0] = 0;
+
+	/* positive normals */
+	for(i = 1; i < 32; ++i)
+		util_half_to_float_offset_table[i] = 1024;
+
+	/* negative zero or denormals */
+	util_half_to_float_offset_table[32] = 0;
+
+	/* negative normals */
+	for(i = 33; i < 64; ++i)
+		util_half_to_float_offset_table[i] = 1024;
+
+
+
+	/* very small numbers mapping to zero */
+	for(i = -127; i < -24; ++i) {
+		util_float_to_half_base_table[127 + i] = 0;
+		util_float_to_half_shift_table[127 + i] = 24;
+	}
+
+	/* small numbers mapping to denormals */
+	for(i = -24; i < -14; ++i) {
+		util_float_to_half_base_table[127 + i] = 0x0400 >> (-14 - i);
+		util_float_to_half_shift_table[127 + i] = -i - 1;
+	}
+
+	/* normal numbers */
+	for(i = -14; i < 16; ++i) {
+		util_float_to_half_base_table[127 + i] = (i + 15) << 10;
+		util_float_to_half_shift_table[127 + i] = 13;
+	}
+
+	/* large numbers mapping to infinity */
+	for(i = 16; i < 128; ++i) {
+		util_float_to_half_base_table[127 + i] = 0x7c00;
+		util_float_to_half_shift_table[127 + i] = 24;
+	}
+
+	/* infinity and NaNs */
+	util_float_to_half_base_table[255] = 0x7c00;
+	util_float_to_half_shift_table[255] = 13;
+
+	/* negative numbers */
+	for(i = 0; i < 256; ++i) {
+		util_float_to_half_base_table[256 + i] = util_float_to_half_base_table[i] | 0x8000;
+		util_float_to_half_shift_table[256 + i] = util_float_to_half_shift_table[i];
+	}
+}
diff --git a/src/gallium/auxiliary/util/u_half.h b/src/gallium/auxiliary/util/u_half.h
new file mode 100644
index 0000000000..464d43df8a
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_half.h
@@ -0,0 +1,55 @@
+#ifndef U_HALF_H
+#define U_HALF_H
+
+#include "pipe/p_compiler.h"
+
+extern uint32_t util_half_to_float_mantissa_table[2048];
+extern uint32_t util_half_to_float_exponent_table[64];
+extern uint32_t util_half_to_float_offset_table[64];
+extern uint16_t util_float_to_half_base_table[512];
+extern uint8_t util_float_to_half_shift_table[512];
+
+/*
+ * Note that if the half float is a signaling NaN, the x87 FPU will turn
+ * it into a quiet NaN immediately upon loading into a float.
+ *
+ * Additionally, denormals may be flushed to zero.
+ *
+ * To avoid this, use the floatui functions instead of the float ones
+ * when just doing conversion rather than computation on the resulting
+ * floats.
+ */
+
+static INLINE uint32_t
+util_half_to_floatui(half h)
+{
+	unsigned exp = h >> 10;
+	return util_half_to_float_mantissa_table[util_half_to_float_offset_table[exp] + (h & 0x3ff)]
+		+ util_half_to_float_exponent_table[exp];
+}
+
+static INLINE float
+util_half_to_float(half h)
+{
+	union {float f; uint32_t v;} r;
+	r.v = util_half_to_floatui(h);
+	return r.f;
+}
+
+static INLINE half
+util_floatui_to_half(uint32_t v)
+{
+	unsigned signexp = v >> 23;
+	return util_float_to_half_base_table[signexp]
+		+ ((v & 0x007fffff) >> util_float_to_half_shift_table[signexp]);
+}
+
+static INLINE half
+util_float_to_half(float f)
+{
+	union {float f; uint32_t v;} i;
+	i.f = f;
+	return util_floatui_to_half(i.v);
+}
+
+#endif /* U_HALF_H */