1 files changed, 72 insertions, 0 deletions
diff --git a/libc-top-half/musl/src/math/log2f.c b/libc-top-half/musl/src/math/log2f.c
new file mode 100644
index 0000000..c368f88
--- /dev/null
+++ b/libc-top-half/musl/src/math/log2f.c
@@ -0,0 +1,72 @@
+/*
+ * Single-precision log2 function.
+ *
+ * Copyright (c) 2017-2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <math.h>
+#include <stdint.h>
+#include "libm.h"
+#include "log2f_data.h"
+
+/*
+LOG2F_TABLE_BITS = 4
+LOG2F_POLY_ORDER = 4
+
+ULP error: 0.752 (nearest rounding.)
+Relative error: 1.9 * 2^-26 (before rounding.)
+*/
+
+#define N (1 << LOG2F_TABLE_BITS)
+#define T __log2f_data.tab
+#define A __log2f_data.poly
+#define OFF 0x3f330000
+
+float log2f(float x)
+{
+	double_t z, r, r2, p, y, y0, invc, logc;
+	uint32_t ix, iz, top, tmp;
+	int k, i;
+
+	ix = asuint(x);
+	/* Fix sign of zero with downward rounding when x==1.  */
+	if (WANT_ROUNDING && predict_false(ix == 0x3f800000))
+		return 0;
+	if (predict_false(ix - 0x00800000 >= 0x7f800000 - 0x00800000)) {
+		/* x < 0x1p-126 or inf or nan.  */
+		if (ix * 2 == 0)
+			return __math_divzerof(1);
+		if (ix == 0x7f800000) /* log2(inf) == inf.  */
+			return x;
+		if ((ix & 0x80000000) || ix * 2 >= 0xff000000)
+			return __math_invalidf(x);
+		/* x is subnormal, normalize it.  */
+		ix = asuint(x * 0x1p23f);
+		ix -= 23 << 23;
+	}
+
+	/* x = 2^k z; where z is in range [OFF,2*OFF] and exact.
+	   The range is split into N subintervals.
+	   The ith subinterval contains z and c is near its center.  */
+	tmp = ix - OFF;
+	i = (tmp >> (23 - LOG2F_TABLE_BITS)) % N;
+	top = tmp & 0xff800000;
+	iz = ix - top;
+	k = (int32_t)tmp >> 23; /* arithmetic shift */
+	invc = T[i].invc;
+	logc = T[i].logc;
+	z = (double_t)asfloat(iz);
+
+	/* log2(x) = log1p(z/c-1)/ln2 + log2(c) + k */
+	r = z * invc - 1;
+	y0 = logc + (double_t)k;
+
+	/* Pipelined polynomial evaluation to approximate log1p(r)/ln2.  */
+	r2 = r * r;
+	y = A[1] * r + A[2];
+	y = A[0] * r2 + y;
+	p = A[3] * r + y0;
+	y = y * r2 + p;
+	return eval_as_float(y);
+}