converting uint bits back into floats

R=rsc
DELTA=32  (32 added, 0 deleted, 0 changed)
OCL=19084
CL=19091

src/cmd/gc/sys.go

@@ -51,6 +51,8 @@ export func	Inf(int) float64;			// return signed Inf
 export func	NaN() float64;				// return a NaN
 export func	float32bits(float32) uint32;		// raw bits
 export func	float64bits(float64) uint64;		// raw bits
+export func	float32frombits(uint32) float32;		// raw bits
+export func	float64frombits(uint64) float64;		// raw bits
 
 export func	newmap(keysize int, valsize int,
 			keyalg int, valalg int,

src/cmd/gc/sysimport.c

@@ -41,6 +41,8 @@ char *sysimport =
 	"export func sys.NaN () (? float64)\n"
 	"export func sys.float32bits (? float32) (? uint32)\n"
 	"export func sys.float64bits (? float64) (? uint64)\n"
+	"export func sys.float32frombits (? uint32) (? float32)\n"
+	"export func sys.float64frombits (? uint64) (? float64)\n"
 	"export func sys.newmap (keysize int, valsize int, keyalg int, valalg int, hint int) (hmap *map[any] any)\n"
 	"export func sys.mapaccess1 (hmap *map[any] any, key any) (val any)\n"
 	"export func sys.mapaccess2 (hmap *map[any] any, key any) (val any, pres bool)\n"

src/runtime/runtime.c

@@ -204,6 +204,19 @@ float64frombits(uint64 i)
 	return u.f;
 }
 
+static float32
+float32frombits(uint32 i)
+{
+	// The obvious cast-and-pointer code is technically
+	// not valid, and gcc miscompiles it.  Use a union instead.
+	union {
+		float32 f;
+		uint32 i;
+	} u;
+	u.i = i;
+	return u.f;
+}
+
 bool
 isInf(float64 f, int32 sign)
 {
@@ -387,6 +400,21 @@ sys·float64bits(float64 din, uint64 iou)
 	FLUSH(&iou);
 }
 
+// func float32frombits(uint32) float32; // raw bits to float32
+void
+sys·float32frombits(uint32 uin, float32 dou)
+{
+	dou = float32frombits(uin);
+	FLUSH(&dou);
+}
+
+// func float64frombits(uint64) float64; // raw bits to float64
+void
+sys·float64frombits(uint64 uin, float64 dou)
+{
+	dou = float64frombits(uin);
+	FLUSH(&dou);
+}
 
 static int32	argc;
 static uint8**	argv;