fabs

Ответ от Psevdonim[гуру]
man не умеешь что ли?

во-первых, не absf(), absl(), а fabs(), labs()

во-вторых:

> man abs
ABS(3) FreeBSD Library Functions Manual ABS(3)

NAME
abs -- integer absolute value function

LIBRARY
Standard C Library (libc, -lc)

SYNOPSIS
#include <stdlib.h>

int
abs(int j);

DESCRIPTION
The abs() function computes the absolute value of the integer j.
....

> man fabs
FABS(3) FreeBSD Library Functions Manual FABS(3)

NAME
fabs, fabsf, fabsl -- floating-point absolute value functions

LIBRARY
Math Library (libm, -lm)

SYNOPSIS
#include <math.h>

double
fabs(double x);

float
fabsf(float x);

long double
fabsl(long double x);

DESCRIPTION
The fabs(), fabsf() and fabsl() functions compute the absolute value of a
floating-point number x.
....

> man labs
LABS(3) FreeBSD Library Functions Manual LABS(3)

NAME
labs -- return the absolute value of a long integer

LIBRARY
Standard C Library (libc, -lc)

SYNOPSIS
#include <stdlib.h>

long
labs(long j);

DESCRIPTION
The labs() function returns the absolute value of the long integer j.