i think this is posted in the wrong topic, however...

here's your basic lerp (where "l" stands for Linear):

float lerp(float a, float b, float t) {
 return a + (b - a) * t;
}

to convert it to some OTHER response, simply modify t accordingly:

float lerp(float a, float b, float t) {
 t = f(t); // now go define what f() does...
 return a + (b - a) * t;
}

...where f() is some function (preferrably continuous!) giving f(0)=0 and f(1)=1, for example...

for quadratic response:
float f(float t) { return t*t; }

for quintic response:
float f(float t) { return t*t*t*t*t; }

for "circular" response:
float f(float t) { return 1.0-sqrt(1.0-t*t); }

for half-cosine ease-in response:
float f(float t) { return 0.5-cos(t*HALF_PI)*0.5; }

for full-cosine ease-in-out response:
float f(float t) { return 1.0-cos(t*PI); }

keep exploring, you can even use processing's bezier/curve functions:
float f(t) { return bezierPoint(0,0,1,1,t); }
float f(t) { return curvePoint(0,0,1,1,t); }

etcetera