1 files changed, 75 insertions, 0 deletions
diff --git a/pl/math/logf.c b/pl/math/logf.c
new file mode 100644
index 0000000..17a74ed
--- /dev/null
+++ b/pl/math/logf.c
@@ -0,0 +1,75 @@
+/*
+ * Single-precision log function.
+ *
+ * Copyright (c) 2017-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#include <math.h>
+#include <stdint.h>
+#include "math_config.h"
+
+/*
+LOGF_TABLE_BITS = 4
+LOGF_POLY_ORDER = 4
+
+ULP error: 0.818 (nearest rounding.)
+Relative error: 1.957 * 2^-26 (before rounding.)
+*/
+
+#define T __logf_data.tab
+#define A __logf_data.poly
+#define Ln2 __logf_data.ln2
+#define N (1 << LOGF_TABLE_BITS)
+#define OFF 0x3f330000
+
+float
+optr_aor_log_f32 (float x)
+{
+  /* double_t for better performance on targets with FLT_EVAL_METHOD==2.  */
+  double_t z, r, r2, y, y0, invc, logc;
+  uint32_t ix, iz, tmp;
+  int k, i;
+
+  ix = asuint (x);
+#if WANT_ROUNDING
+  /* Fix sign of zero with downward rounding when x==1.  */
+  if (unlikely (ix == 0x3f800000))
+    return 0;
+#endif
+  if (unlikely (ix - 0x00800000 >= 0x7f800000 - 0x00800000))
+    {
+      /* x < 0x1p-126 or inf or nan.  */
+      if (ix * 2 == 0)
+	return __math_divzerof (1);
+      if (ix == 0x7f800000) /* log(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 - LOGF_TABLE_BITS)) % N;
+  k = (int32_t) tmp >> 23; /* arithmetic shift */
+  iz = ix - (tmp & 0x1ff << 23);
+  invc = T[i].invc;
+  logc = T[i].logc;
+  z = (double_t) asfloat (iz);
+
+  /* log(x) = log1p(z/c-1) + log(c) + k*Ln2 */
+  r = z * invc - 1;
+  y0 = logc + (double_t) k * Ln2;
+
+  /* Pipelined polynomial evaluation to approximate log1p(r).  */
+  r2 = r * r;
+  y = A[1] * r + A[2];
+  y = A[0] * r2 + y;
+  y = y * r2 + (y0 + r);
+  return eval_as_float (y);
+}