diff --git a/src/config.rs b/src/config.rs
index e3837d9..c9bec04 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -119,12 +119,6 @@ impl From<LogLevel> for LevelFilter {
     }
 }
 
-// linear mapping between two points
-fn linear_map(x: f64, x1: f64, y1: f64, x2: f64, y2: f64) -> f64 {
-    let m = (y2 - y1) / (x2 - x1);
-    m * (x - x1) + y1
-}
-
 #[derive(Serialize, Deserialize, Debug)]
 pub struct Config {
     log_level: LogLevel,
@@ -147,7 +141,7 @@ impl Config {
             return self.max_speed();
         }
 
-        linear_map(temp, self.speed_matrix[idx].temp, self.speed_matrix[idx].speed, self.speed_matrix[idx+1].temp, self.speed_matrix[idx+1].speed)
+        crate::linear_map(temp, self.speed_matrix[idx].temp, self.speed_matrix[idx+1].temp, self.speed_matrix[idx].speed, self.speed_matrix[idx+1].speed)
     }
 
     pub fn log_level(&self) -> LogLevel {
diff --git a/src/main.rs b/src/main.rs
index bd5f630..892370c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,7 +3,6 @@ mod config;
 extern crate log;
 
 use std::io::ErrorKind;
-use std::cmp::{min, max};
 
 use crate::config::{load_config, Card, Config};
 use gumdrop::Options;
@@ -22,6 +21,12 @@ pub enum AmdFanError {
     FailedReadVendor,
 }
 
+// linear mapping from the xrange to the yrange
+fn linear_map(x: f64, x1: f64, x2: f64, y1: f64, y2: f64) -> f64 {
+    let m = (y2 - y1) / (x2 - x1);
+    m * (x - x1) + y1
+}
+
 #[derive(Debug)]
 pub struct HwMon {
     card: Card,
@@ -124,10 +129,9 @@ impl HwMon {
     }
     
     pub fn set_speed(&mut self, speed: f64) -> std::io::Result<()> {
-        let mut pwm = (speed / 100f64 * 255f64).round() as u32;
-        // stay in the range
-        pwm = max(pwm, self.pwm_min());
-        pwm = min(pwm, self.pwm_max());
+        let min = self.pwm_min() as f64;
+        let max = self.pwm_max() as f64;
+        let pwm = linear_map(speed, 0f64, 100f64, min, max).round() as u32;
         self.set_pwm(pwm)
     }