Simple peak follower

Type : amplitude analysis
References : Posted by Phil Burk
Notes :
This simple peak follower will give track the peaks of a signal. It will rise rapidly when the input is rising, and then decay exponentially when the input drops. It can be used to drive VU meters, or used in an automatic gain control circuit.
Code :
// halfLife = time in seconds for output to decay to half value after an impulse

static float output = 0.0;

float scalar = pow( 0.5, 1.0/(halfLife * sampleRate)));

if( input < 0.0 )
  input = -input;  /* Absolute value. */

if ( input >= output )
{
   /* When we hit a peak, ride the peak to the top. */
   output = input;
}
else
{
   /* Exponential decay of output when signal is low. */
   output = output * scalar;
   /*
   ** When current gets close to 0.0, set current to 0.0 to prevent FP underflow
   ** which can cause a severe performance degradation due to a flood
   ** of interrupts.
   */
   if( output < VERY_SMALL_FLOAT ) output = 0.0;
}

Comments
from : marianomazzeo[AT]hotmail[DOT]com
comment : Totally newby question. What apis are you using for this code?

from : cafreamoroso[AT]gmail[DOT]com
comment : #ifndef VERY_SMALL_FLOAT #define VERY_SMALL_FLOAT 1.0e-30F #endif