math: ilogb cleanup

* consistent code style
* explicit union instead of typedef for double and float bit access
* turn FENV_ACCESS ON to make 0/0.0f raise invalid flag
* (untested) ld128 version of ilogbl (used by logbl which has ld128 support)

src/math/ilogb.c

@@ -3,22 +3,24 @@
 
 int ilogb(double x)
 {
-	union dshape u = {x};
-	int e = u.bits>>52 & 0x7ff;
+	#pragma STDC FENV_ACCESS ON
+	union {double f; uint64_t i;} u = {x};
+	uint64_t i = u.i;
+	int e = i>>52 & 0x7ff;
 
 	if (!e) {
-		u.bits <<= 12;
-		if (u.bits == 0) {
+		i <<= 12;
+		if (i == 0) {
 			FORCE_EVAL(0/0.0f);
 			return FP_ILOGB0;
 		}
 		/* subnormal x */
-		for (e = -0x3ff; u.bits < (uint64_t)1<<63; e--, u.bits<<=1);
+		for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
 		return e;
 	}
 	if (e == 0x7ff) {
 		FORCE_EVAL(0/0.0f);
-		return u.bits<<12 ? FP_ILOGBNAN : INT_MAX;
+		return i<<12 ? FP_ILOGBNAN : INT_MAX;
 	}
 	return e - 0x3ff;
 }

src/math/ilogbf.c

@@ -3,22 +3,24 @@
 
 int ilogbf(float x)
 {
-	union fshape u = {x};
-	int e = u.bits>>23 & 0xff;
+	#pragma STDC FENV_ACCESS ON
+	union {float f; uint32_t i;} u = {x};
+	uint32_t i = u.i;
+	int e = i>>23 & 0xff;
 
 	if (!e) {
-		u.bits <<= 9;
-		if (u.bits == 0) {
+		i <<= 9;
+		if (i == 0) {
 			FORCE_EVAL(0/0.0f);
 			return FP_ILOGB0;
 		}
 		/* subnormal x */
-		for (e = -0x7f; u.bits < (uint32_t)1<<31; e--, u.bits<<=1);
+		for (e = -0x7f; i>>31 == 0; e--, i<<=1);
 		return e;
 	}
 	if (e == 0xff) {
 		FORCE_EVAL(0/0.0f);
-		return u.bits<<9 ? FP_ILOGBNAN : INT_MAX;
+		return i<<9 ? FP_ILOGBNAN : INT_MAX;
 	}
 	return e - 0x7f;
 }

src/math/ilogbl.c

@@ -9,23 +9,46 @@ int ilogbl(long double x)
 #elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
 int ilogbl(long double x)
 {
+	#pragma STDC FENV_ACCESS ON
 	union ldshape u = {x};
 	uint64_t m = u.i.m;
 	int e = u.i.se & 0x7fff;
 
 	if (!e) {
 		if (m == 0) {
-			FORCE_EVAL(x/x);
+			FORCE_EVAL(0/0.0f);
 			return FP_ILOGB0;
 		}
 		/* subnormal x */
-		for (e = -0x3fff+1; m < (uint64_t)1<<63; e--, m<<=1);
+		for (e = -0x3fff+1; m>>63 == 0; e--, m<<=1);
 		return e;
 	}
 	if (e == 0x7fff) {
 		FORCE_EVAL(0/0.0f);
-		/* in ld80 msb is set in inf */
-		return m << 1 ? FP_ILOGBNAN : INT_MAX;
+		return m<<1 ? FP_ILOGBNAN : INT_MAX;
+	}
+	return e - 0x3fff;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+int ilogbl(long double x)
+{
+	#pragma STDC FENV_ACCESS ON
+	union ldshape u = {x};
+	int e = u.i.se & 0x7fff;
+
+	if (!e) {
+		if (x == 0) {
+			FORCE_EVAL(0/0.0f);
+			return FP_ILOGB0;
+		}
+		/* subnormal x */
+		x *= 0x1p120;
+		return ilogbl(x) - 120;
+	}
+	if (e == 0x7fff) {
+		FORCE_EVAL(0/0.0f);
+		u.i.se = 0;
+		return u.f ? FP_ILOGBNAN : INT_MAX;
 	}
 	return e - 0x3fff;
 }