Adding upstream version 0.0~git20221206.8b7148f.upstream/0.0_git20221206.8b7148f

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 122 insertions, 0 deletions

diff --git a/libc-top-half/musl/src/math/log2.c b/libc-top-half/musl/src/math/log2.c
new file mode 100644
index 0000000..1276ed4
--- /dev/null
+++ b/libc-top-half/musl/src/math/log2.c
@@ -0,0 +1,122 @@
+/*
+ * Double-precision log2(x) function.
+ *
+ * Copyright (c) 2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <math.h>
+#include <stdint.h>
+#include "libm.h"
+#include "log2_data.h"
+
+#define T __log2_data.tab
+#define T2 __log2_data.tab2
+#define B __log2_data.poly1
+#define A __log2_data.poly
+#define InvLn2hi __log2_data.invln2hi
+#define InvLn2lo __log2_data.invln2lo
+#define N (1 << LOG2_TABLE_BITS)
+#define OFF 0x3fe6000000000000
+
+/* Top 16 bits of a double.  */
+static inline uint32_t top16(double x)
+{
+	return asuint64(x) >> 48;
+}
+
+double log2(double x)
+{
+	double_t z, r, r2, r4, y, invc, logc, kd, hi, lo, t1, t2, t3, p;
+	uint64_t ix, iz, tmp;
+	uint32_t top;
+	int k, i;
+
+	ix = asuint64(x);
+	top = top16(x);
+#define LO asuint64(1.0 - 0x1.5b51p-5)
+#define HI asuint64(1.0 + 0x1.6ab2p-5)
+	if (predict_false(ix - LO < HI - LO)) {
+		/* Handle close to 1.0 inputs separately.  */
+		/* Fix sign of zero with downward rounding when x==1.  */
+		if (WANT_ROUNDING && predict_false(ix == asuint64(1.0)))
+			return 0;
+		r = x - 1.0;
+#if __FP_FAST_FMA
+		hi = r * InvLn2hi;
+		lo = r * InvLn2lo + __builtin_fma(r, InvLn2hi, -hi);
+#else
+		double_t rhi, rlo;
+		rhi = asdouble(asuint64(r) & -1ULL << 32);
+		rlo = r - rhi;
+		hi = rhi * InvLn2hi;
+		lo = rlo * InvLn2hi + r * InvLn2lo;
+#endif
+		r2 = r * r; /* rounding error: 0x1p-62.  */
+		r4 = r2 * r2;
+		/* Worst-case error is less than 0.54 ULP (0.55 ULP without fma).  */
+		p = r2 * (B[0] + r * B[1]);
+		y = hi + p;
+		lo += hi - y + p;
+		lo += r4 * (B[2] + r * B[3] + r2 * (B[4] + r * B[5]) +
+			    r4 * (B[6] + r * B[7] + r2 * (B[8] + r * B[9])));
+		y += lo;
+		return eval_as_double(y);
+	}
+	if (predict_false(top - 0x0010 >= 0x7ff0 - 0x0010)) {
+		/* x < 0x1p-1022 or inf or nan.  */
+		if (ix * 2 == 0)
+			return __math_divzero(1);
+		if (ix == asuint64(INFINITY)) /* log(inf) == inf.  */
+			return x;
+		if ((top & 0x8000) || (top & 0x7ff0) == 0x7ff0)
+			return __math_invalid(x);
+		/* x is subnormal, normalize it.  */
+		ix = asuint64(x * 0x1p52);
+		ix -= 52ULL << 52;
+	}
+
+	/* 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 >> (52 - LOG2_TABLE_BITS)) % N;
+	k = (int64_t)tmp >> 52; /* arithmetic shift */
+	iz = ix - (tmp & 0xfffULL << 52);
+	invc = T[i].invc;
+	logc = T[i].logc;
+	z = asdouble(iz);
+	kd = (double_t)k;
+
+	/* log2(x) = log2(z/c) + log2(c) + k.  */
+	/* r ~= z/c - 1, |r| < 1/(2*N).  */
+#if __FP_FAST_FMA
+	/* rounding error: 0x1p-55/N.  */
+	r = __builtin_fma(z, invc, -1.0);
+	t1 = r * InvLn2hi;
+	t2 = r * InvLn2lo + __builtin_fma(r, InvLn2hi, -t1);
+#else
+	double_t rhi, rlo;
+	/* rounding error: 0x1p-55/N + 0x1p-65.  */
+	r = (z - T2[i].chi - T2[i].clo) * invc;
+	rhi = asdouble(asuint64(r) & -1ULL << 32);
+	rlo = r - rhi;
+	t1 = rhi * InvLn2hi;
+	t2 = rlo * InvLn2hi + r * InvLn2lo;
+#endif
+
+	/* hi + lo = r/ln2 + log2(c) + k.  */
+	t3 = kd + logc;
+	hi = t3 + t1;
+	lo = t3 - hi + t1 + t2;
+
+	/* log2(r+1) = r/ln2 + r^2*poly(r).  */
+	/* Evaluation is optimized assuming superscalar pipelined execution.  */
+	r2 = r * r; /* rounding error: 0x1p-54/N^2.  */
+	r4 = r2 * r2;
+	/* Worst-case error if |y| > 0x1p-4: 0.547 ULP (0.550 ULP without fma).
+	   ~ 0.5 + 2/N/ln2 + abs-poly-error*0x1p56 ULP (+ 0.003 ULP without fma).  */
+	p = A[0] + r * A[1] + r2 * (A[2] + r * A[3]) + r4 * (A[4] + r * A[5]);
+	y = lo + r2 * p + hi;
+	return eval_as_double(y);
+}