Add support for in-memory half float data. Fixes issue #10

tests/half-1.ispc

@@ -0,0 +1,21 @@
+
+export uniform int width() { return programCount; }
+
+export void f_v(uniform float RET[]) {
+    float sum = 0;
+    int errors = 0;
+    for (uniform int i = 0; i <= 0xffff; ++i) {
+        uniform unsigned int16 h = i;
+        uniform float f = half_to_float(i);
+        h = float_to_half(f);
+
+        // may return a different value back for NaNs..
+        if (f == f && i != h)
+            ++errors;
+    }
+    RET[programIndex] = errors;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 0;
+}

tests/half.ispc

@@ -0,0 +1,21 @@
+
+export uniform int width() { return programCount; }
+
+export void f_v(uniform float RET[]) {
+    float sum = 0;
+    int errors = 0;
+    for (uniform int i = 0; i <= 0xffff; ++i) {
+        unsigned int16 h = i;
+        float f = half_to_float(i);
+        h = float_to_half(f);
+
+        // may return a different value back for NaNs..
+        if (f == f && i != h)
+            ++errors;
+    }
+    RET[programIndex] = errors;
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 0;
+}