Modern Math Log1p

Home › Math Library › Math Library › Log1p

Log1p

Returns the natural logarithm of one plus a number, accurately near zero.

Syntax

Log1p( x )

Notes

• For a tiny x, 1.0 + x rounds to 1 before the logarithm sees it. Log1p never forms that sum.
• Expm1 is its inverse; -1 gives minus infinity.
• Overloaded on float64 and on float32: a single-precision argument takes the single-precision path and does not widen.
• BOUNDED accuracy: correct to the platform library's stated ulp bound.

Examples

#import "std/numeric"
using numeric

print Log1p( 1e-17 )         '' 1e-017
print log( 1.0 + 1e-17 )     '' 0 -- the 1.0 swallowed it
print Log1p( -1.0 )          '' -1.#INF

---

Library: Math Library
Category: Math Library
Documented under: The libm surface