1 files changed, 49 insertions, 0 deletions
diff --git a/pl/math/v_expm1f_inline.h b/pl/math/v_expm1f_inline.h
new file mode 100644
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--- /dev/null
+++ b/pl/math/v_expm1f_inline.h
@@ -0,0 +1,49 @@
+/*
+ * Helper for single-precision routines which calculate exp(x) - 1 and do not
+ * need special-case handling
+ *
+ * Copyright (c) 2022-2023, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef PL_MATH_V_EXPM1F_INLINE_H
+#define PL_MATH_V_EXPM1F_INLINE_H
+
+#include "v_math.h"
+#include "math_config.h"
+#include "estrinf.h"
+
+#define One 0x3f800000
+#define Shift v_f32 (0x1.8p23f)
+#define InvLn2 v_f32 (0x1.715476p+0f)
+#define MLn2hi v_f32 (-0x1.62e4p-1f)
+#define MLn2lo v_f32 (-0x1.7f7d1cp-20f)
+
+#define C(i) v_f32 (__expm1f_poly[i])
+
+static inline v_f32_t
+expm1f_inline (v_f32_t x)
+{
+  /* Helper routine for calculating exp(x) - 1.
+     Copied from v_expm1f_1u6.c, with all special-case handling removed - the
+     calling routine should handle special values if required.  */
+
+  /* Reduce argument: f in [-ln2/2, ln2/2], i is exact.  */
+  v_f32_t j = v_fma_f32 (InvLn2, x, Shift) - Shift;
+  v_s32_t i = v_to_s32_f32 (j);
+  v_f32_t f = v_fma_f32 (j, MLn2hi, x);
+  f = v_fma_f32 (j, MLn2lo, f);
+
+  /* Approximate expm1(f) with polynomial P, expm1(f) ~= f + f^2 * P(f).
+     Uses Estrin scheme, where the main __v_expm1f routine uses Horner.  */
+  v_f32_t f2 = f * f;
+  v_f32_t p = ESTRIN_4 (f, f2, f2 * f2, C);
+  p = v_fma_f32 (f2, p, f);
+
+  /* t = 2^i.  */
+  v_f32_t t = v_as_f32_u32 (v_as_u32_s32 (i << 23) + One);
+  /* expm1(x) ~= p * t + (t - 1).  */
+  return v_fma_f32 (p, t, t - 1);
+}
+
+#endif // PL_MATH_V_EXPM1F_INLINE_H