profiling/timing: implement execution time profiler

Author: tmrts

README.md

@@ -98,7 +98,7 @@ A curated collection of idiomatic design & application patterns for Go language.
 
 | Pattern | Description | Status |
 |:-------:|:----------- |:------:|
-| [Timing Functions](/profiling/timing.md) | Wraps a function and logs the execution | ✘ |
+| [Timing Functions](/profiling/timing.md) | Wraps a function and logs the execution | ✔ |
 
 ## Idioms
 

profiling/timing.md

@@ -0,0 +1,38 @@
+# Timing Functions
+
+When optimizing code, sometimes a quick and dirty time measurement is required
+as opposed to utilizing profiler tools/frameworks to validate assumptions.
+
+Time measurements can be performed by utilizing `time` package and `defer` statements.
+
+## Implementation
+
+```go
+package profile
+
+import (
+    "time"
+    "log"
+)
+
+func Duration(invocation time.Time, name string) {
+    elapsed := time.Since(invocation)
+
+    log.Printf("%s lasted %s", name, elapsed)
+}
+```
+
+## Usage
+
+```go
+func IntFactorial(x big.Int) *big.Int {
+    defer profile.Duration(time.Now(), "IntFactorial")
+
+    y := big.NewInt(1)
+    for one := big.NewInt(1); x.Sign() > 0; x.Sub(x, one) {
+        y.Mul(y, x)
+    }
+
+    return x.Set(y)
+}
+```