add Brady's better write_sane_extended()

1 files changed, 21 insertions, 18 deletions

diff --git a/src/test_streams/main.c b/src/test_streams/main.c
index 82384adc..71c8feea 100644
--- a/src/test_streams/main.c
+++ b/src/test_streams/main.c
@@ -141,33 +141,36 @@ static FLAC__bool write_big_endian_int32(FILE *f, FLAC__int32 x)
 #endif
 
 static FLAC__bool write_sane_extended(FILE *f, unsigned val)
-{
-	unsigned i, exponent;
-
-	/* this reasonable limitation make the implementation simpler */
-	FLAC__ASSERT(val < 0x80000000);
-
-	/* we'll use the denormalized form, with no implicit '1' (i bit == 0) */
-
-	for(i = val, exponent = 0; i; i >>= 1, exponent++)
+	/* Write to 'f' a SANE extended representation of 'val'.  Return false if
+	* the write succeeds; return true otherwise.
+	*
+	* SANE extended is an 80-bit IEEE-754 representation with sign bit, 15 bits
+	* of exponent, and 64 bits of significand (mantissa).  Unlike most IEEE-754
+	* representations, it does not imply a 1 above the MSB of the significand.
+	*
+	* Preconditions:
+	*  val!=0U
+	*/
+{
+	unsigned int shift, exponent;
+
+	FLAC__ASSERT(val!=0U); /* handling 0 would require a special case */
+
+	for(shift= 0U; (val>>(31-shift))==0U; ++shift)
 		;
-	if(!write_big_endian_uint16(f, (FLAC__uint16)(exponent + 16383)))
-		return false;
+	val<<= shift;
+	exponent= 63U-(shift+32U); /* add 32 for unused second word */
 
-	for(i = 32; i; i--) {
-		if(val & 0x40000000)
-			break;
-		val <<= 1;
-	}
+	if(!write_big_endian_uint16(f, (FLAC__uint16)(exponent+0x3FFF)))
+		return false;
 	if(!write_big_endian_uint32(f, val))
 		return false;
-	if(!write_big_endian_uint32(f, 0))
+	if(!write_big_endian_uint32(f, 0)) /* unused second word */
 		return false;
 
 	return true;
 }
 
-
 /* a mono one-sample 16bps stream */
 static FLAC__bool generate_01()
 {