dix: add utility functions for double to/fro FP1616/FP3232 conversion

Co-authored-by: Jeremy Huddleston <jeremyhu@apple.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/dix/inpututils.c b/dix/inpututils.c
index 0a3d3d8b4..cd4577347 100644
--- a/dix/inpututils.c
+++ b/dix/inpututils.c
@@ -759,3 +759,66 @@ input_option_set_value(InputOption *opt, const char *value)
     if (value)
         opt->value = strdup(value);
 }
+
+
+/* FP1616/FP3232 conversion functions.
+ * Fixed point types are encoded as signed integral and unsigned frac. So any
+ * negative number -n.m is encoded as floor(n) + (1 - 0.m).
+ */
+double
+fp1616_to_double(FP1616 in)
+{
+    double ret;
+
+    ret  = (double)(in >> 16);
+    ret += (double)(in & 0xffff) * (1.0 / (1UL << 16)); /* Optimized: ldexp((double)(in & 0xffff), -16); */
+    return ret;
+}
+
+double
+fp3232_to_double(FP3232 in)
+{
+    double ret;
+    ret  = (double)in.integral;
+    ret += (double)in.frac * (1.0 / (1ULL << 32)); /* Optimized: ldexp((double)in.frac, -32); */
+    return ret;
+}
+
+
+FP1616
+double_to_fp1616(double in)
+{
+    FP1616 ret;
+    int32_t integral;
+    double tmp;
+    uint32_t frac_d;
+
+    tmp = floor(in);
+    integral = (int32_t)tmp;
+
+    tmp = (in - integral) * (1UL << 16); /* Optimized: ldexp(in - integral, 16) */
+    frac_d = (uint16_t)tmp;
+
+    ret = integral << 16;
+    ret |= frac_d & 0xffff;
+    return ret;
+}
+
+FP3232
+double_to_fp3232(double in)
+{
+    FP3232 ret;
+    int32_t integral;
+    double tmp;
+    uint32_t frac_d;
+
+    tmp = floor(in);
+    integral = (int32_t)tmp;
+
+    tmp = (in - integral) * (1ULL << 32); /* Optimized: ldexp(in - integral, 32) */
+    frac_d = (uint32_t)tmp;
+
+    ret.integral = integral;
+    ret.frac = frac_d;
+    return ret;
+}