1 files changed, 98 insertions, 0 deletions
diff --git a/src/mesa/drivers/dri/savage/savagespan.h b/src/mesa/drivers/dri/savage/savagespan.h
index 35247b4706..cb3a1b52fd 100644
--- a/src/mesa/drivers/dri/savage/savagespan.h
+++ b/src/mesa/drivers/dri/savage/savagespan.h
@@ -27,4 +27,102 @@
 
 extern void savageDDInitSpanFuncs( GLcontext *ctx );
 
+/*
+ * Savage 16-bit float depth format with zExpOffset=16:
+ *   4 bit unsigned exponent, 12 bit mantissa
+ *
+ * The meaning of the mantissa is different from IEEE floatint point
+ * formats. The same number can't be encoded with different exponents.
+ * So no bits are wasted.
+ *
+ * exponent | range encoded by mantissa | accuracy or mantissa
+ * ---------+---------------------------+---------------------
+ *       15 | 2^-1 .. 1                 | 2^-13
+ *       14 | 2^-2 .. 2^-1              | 2^-14
+ *       13 | 2^-3 .. 2^-2              | 2^-15
+ *      ... | ...                       |
+ *        2 | 2^-14 .. 2^-13            | 2^-27
+ *        1 | 2^-15 .. 2^-14            | 2^-27
+ *        0 | 2^-16 .. 2^-15            | 2^-28
+ *
+ * Note that there is no encoding for numbers < 2^-16.
+ */
+static __inline GLuint savageEncodeFloat16( GLdouble x )
+{
+    GLint r = (GLint)(x * 0x10000000);
+    GLint exp = 0;
+    if (r < 0x1000)
+	return 0;
+    while (r - 0x1000 > 0x0fff) {
+	r >>= 1;
+	exp++;
+    }
+    return exp > 0xf ? 0xffff : (r - 0x1000) | (exp << 12);
+}
+static __inline GLdouble savageDecodeFloat16( GLuint x )
+{
+    static const GLdouble pow2[16] = {
+	1.0/(1<<28), 1.0/(1<<27), 1.0/(1<<26), 1.0/(1<<25),
+	1.0/(1<<24), 1.0/(1<<23), 1.0/(1<<22), 1.0/(1<<21),
+	1.0/(1<<20), 1.0/(1<<19), 1.0/(1<<18), 1.0/(1<<17),
+	1.0/(1<<16), 1.0/(1<<15), 1.0/(1<<14), 1.0/(1<<13)
+    };
+    static const GLdouble bias[16] = {
+	1.0/(1<<16), 1.0/(1<<15), 1.0/(1<<14), 1.0/(1<<13),
+	1.0/(1<<12), 1.0/(1<<11), 1.0/(1<<10), 1.0/(1<< 9),
+	1.0/(1<< 8), 1.0/(1<< 7), 1.0/(1<< 6), 1.0/(1<< 5),
+	1.0/(1<< 4), 1.0/(1<< 3), 1.0/(1<< 2), 1.0/(1<< 1)
+    };
+    GLuint mant = x & 0x0fff;
+    GLuint exp = (x >> 12) & 0xf;
+    return bias[exp] + pow2[exp]*mant;
+}
+
+/*
+ * Savage 24-bit float depth format with zExpOffset=32:
+ *   5 bit unsigned exponent, 19 bit mantissa
+ *
+ * Details analogous to the 16-bit format.
+ */
+static __inline GLuint savageEncodeFloat24( GLdouble x )
+{
+    int64_t r = (int64_t)(x * ((int64_t)1 << (19+32)));
+    GLint exp = 0;
+    if (r < 0x80000)
+	return 0;
+    while (r - 0x80000 > 0x7ffff) {
+	r >>= 1;
+	exp++;
+    }
+    return exp > 0x1f ? 0xffffff : (r - 0x80000) | (exp << 19);
+}
+#define _1 (int64_t)1
+static __inline GLdouble savageDecodeFloat24( GLuint x )
+{
+    static const GLdouble pow2[32] = {
+	1.0/(_1<<51), 1.0/(_1<<50), 1.0/(_1<<49), 1.0/(_1<<48),
+	1.0/(_1<<47), 1.0/(_1<<46), 1.0/(_1<<45), 1.0/(_1<<44),
+	1.0/(_1<<43), 1.0/(_1<<42), 1.0/(_1<<41), 1.0/(_1<<40),
+	1.0/(_1<<39), 1.0/(_1<<38), 1.0/(_1<<37), 1.0/(_1<<36),
+	1.0/(_1<<35), 1.0/(_1<<34), 1.0/(_1<<33), 1.0/(_1<<32),
+	1.0/(_1<<31), 1.0/(_1<<30), 1.0/(_1<<29), 1.0/(_1<<28),
+	1.0/(_1<<27), 1.0/(_1<<26), 1.0/(_1<<25), 1.0/(_1<<24),
+	1.0/(_1<<23), 1.0/(_1<<22), 1.0/(_1<<21), 1.0/(_1<<20)
+    };
+    static const GLdouble bias[32] = {
+	1.0/(_1<<32), 1.0/(_1<<31), 1.0/(_1<<30), 1.0/(_1<<29),
+	1.0/(_1<<28), 1.0/(_1<<27), 1.0/(_1<<26), 1.0/(_1<<25),
+	1.0/(_1<<24), 1.0/(_1<<23), 1.0/(_1<<22), 1.0/(_1<<21),
+	1.0/(_1<<20), 1.0/(_1<<19), 1.0/(_1<<18), 1.0/(_1<<17),
+	1.0/(_1<<16), 1.0/(_1<<15), 1.0/(_1<<14), 1.0/(_1<<13),
+	1.0/(_1<<12), 1.0/(_1<<11), 1.0/(_1<<10), 1.0/(_1<< 9),
+	1.0/(_1<< 8), 1.0/(_1<< 7), 1.0/(_1<< 6), 1.0/(_1<< 5),
+	1.0/(_1<< 4), 1.0/(_1<< 3), 1.0/(_1<< 2), 1.0/(_1<< 1)
+    };
+    GLuint mant = x & 0x7ffff;
+    GLuint exp = (x >> 19) & 0x1f;
+    return bias[exp] + pow2[exp]*mant;
+}
+#undef _1
+
 #endif