If PHP is built without complete ANSI C prototypes in scope the 'round' function can fail.

This is because the second argument to 'pow' in ext/standard/math.c:143 is an integer, and without prototypes it doesn't receive its implicit cast to a double, causing the 'pow' function to receive an undefined value on the stack.

The simple fix is to put an explicit (double) cast in:

    f = pow(10.0, (double)places);

A better fix might be to ensure that the ANSI version of the prototypes from <math.h> are always in scope, but that may be difficult to achieve across a wide variety of systems.