uobject: Add support for float properties.

[upkg.git] / src / uobject / uobject.c

diff --git a/src/uobject/uobject.c b/src/uobject/uobject.c
index a0826902d5a029998b807da9486a2ef112b02538..627abe68e32ac3dc2405a1887fd3ad85178e4d10 100644 (file)
--- a/src/uobject/uobject.c
+++ b/src/uobject/uobject.c
@@ -19,6 +19,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <inttypes.h>
@@ -299,6 +300,41 @@ static int decode_object_property(UObject *uo, GValue *val, unsigned long len)
        return 0;
 }
 
+/*
+ * Deserialize an IEEE 754 binary32 value in "little endian" (for whatever
+ * that term is worth in this context).  That is, when interpreted as a little
+ * endian 32-bit unsigned integer: bit 31 is the sign, bits 30-23 are the
+ * (biased) exponent, and bits 22-0 are the encoded part of the significand.
+ *
+ * The implementation is designed to be agnostic of the platform's actual
+ * float type, but the conversion may be lossy if "float" is not itself a
+ * binary32 format.  NaN payloads are not preserved.
+ */
+static float unpack_binary32_le(const unsigned char *buf)
+{
+       unsigned long raw;
+       long significand;
+       int exponent;
+       float result;
+
+       raw = unpack_32_le(buf);
+       exponent = (raw & 0x7f800000) >> 23;
+       significand = (raw & 0x007fffff) >> 0;
+
+       switch (exponent) {
+       case 255:
+               result = significand ? NAN : INFINITY;
+               break;
+       default:
+               significand |= 0x00800000;
+               /* fall through */
+       case 0:
+               result = ldexpf(significand, exponent-126-24);
+       }
+
+       return copysignf(result, raw & 0x80000000 ? -1 : 1);
+}
+
 static unsigned long deserialize_property(UObject *uo, struct prop_head *head)
 {
        struct u_object_priv *priv = U_OBJECT_GET_PRIV(uo);
@@ -340,6 +376,13 @@ static unsigned long deserialize_property(UObject *uo, struct prop_head *head)
                        return 0;
                g_object_set_property(G_OBJECT(uo), head->prop_name, &val);
                break;
+       case PROPERTY_FLOAT:
+               if (head->size != 4 || priv->nbuf-len < head->size)
+                       return 0;
+               g_value_init(&val, G_TYPE_FLOAT);
+               g_value_set_float(&val, unpack_binary32_le(priv->buf+len));
+               g_object_set_property(G_OBJECT(uo), head->prop_name, &val);
+               break;
        default:
                u_warn(uo, "%s: unsupported property type %u",
                           head->prop_name, (unsigned)head->type);