math: cleanup exp2.c exp2f.c and exp2l.c

* old code relied on sign extension on right shift
* exp2l ld64 wrapper was wrong
* use scalbn instead of bithacks

1 files changed, 14 insertions, 16 deletions

diff --git a/src/math/exp2f.c b/src/math/exp2f.c
index 55c22eac..279f32de 100644
--- a/src/math/exp2f.c
+++ b/src/math/exp2f.c
@@ -27,19 +27,15 @@
 
 #include "libm.h"
 
-#define TBLBITS 4
-#define TBLSIZE (1 << TBLBITS)
+#define TBLSIZE 16
 
 static const float
-huge  = 0x1p100f,
 redux = 0x1.8p23f / TBLSIZE,
 P1    = 0x1.62e430p-1f,
 P2    = 0x1.ebfbe0p-3f,
 P3    = 0x1.c6b348p-5f,
 P4    = 0x1.3b2c9cp-7f;
 
-static const volatile float twom100 = 0x1p-100f;
-
 static const double exp2ft[TBLSIZE] = {
   0x1.6a09e667f3bcdp-1,
   0x1.7a11473eb0187p-1,
@@ -89,23 +85,25 @@ float exp2f(float x)
 {
 	double tv, twopk, u, z;
 	float t;
-	uint32_t hx, ix, i0;
-	int32_t k;
+	uint32_t hx, ix, i0, k;
 
 	/* Filter out exceptional cases. */
 	GET_FLOAT_WORD(hx, x);
 	ix = hx & 0x7fffffff;
 	if (ix >= 0x43000000) {  /* |x| >= 128 */
 		if (ix >= 0x7f800000) {
-			if ((ix & 0x7fffff) != 0 || (hx & 0x80000000) == 0)
-				return x + x; /* x is NaN or +Inf */
-			else
-				return 0.0;   /* x is -Inf */
+			if (hx == 0xff800000) /* -inf */
+				return 0;
+			return x;
+		}
+		if (x >= 128) {
+			STRICT_ASSIGN(float, x, x * 0x1p127);
+			return x;
+		}
+		if (x <= -150) {
+			STRICT_ASSIGN(float, x, 0x1p-100*0x1p-100);
+			return x;
 		}
-		if (x >= 0x1.0p7f)
-			return huge * huge;   /* overflow */
-		if (x <= -0x1.2cp7f)
-			return twom100 * twom100; /* underflow */
 	} else if (ix <= 0x33000000) {  /* |x| <= 0x1p-25 */
 		return 1.0f + x;
 	}
@@ -114,7 +112,7 @@ float exp2f(float x)
 	STRICT_ASSIGN(float, t, x + redux);
 	GET_FLOAT_WORD(i0, t);
 	i0 += TBLSIZE / 2;
-	k = (i0 >> TBLBITS) << 20;
+	k = (i0 / TBLSIZE) << 20;
 	i0 &= TBLSIZE - 1;
 	t -= redux;
 	z = x - t;