Add BigToCompact example.

README.md

@@ -84,9 +84,14 @@ is by no means exhaustive:
 
 * [CompactToBig Example]
   (http://godoc.org/github.com/conformal/btcchain#example-CompactToBig)  
-  Demonstrates how to convert the "bits" in a block header which represent the
-  target difficulty to a big integer and display it using the typical hex
-  notation.
+  Demonstrates how to convert the compact "bits" in a block header which
+  represent the target difficulty to a big integer and display it using the
+  typical hex notation.
+
+* [BigToCompact Example]
+  (http://godoc.org/github.com/conformal/btcchain#example-BigToCompact)  
+  Demonstrates how to convert how to convert a target difficulty into the
+  compact "bits" in a block header which represent that target difficulty.
 
 ## TODO
 

example_test.go

@@ -11,6 +11,7 @@ import (
 	_ "github.com/conformal/btcdb/memdb"
 	"github.com/conformal/btcnet"
 	"github.com/conformal/btcutil"
+	"math/big"
 )
 
 // This example demonstrates how to create a new chain instance and use
@@ -58,9 +59,9 @@ func ExampleBlockChain_ProcessBlock() {
 	// Failed to process block: already have block 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
 }
 
-// This example demonstrates how to convert the "bits" in a block header which
-// represent the target difficulty to a big integer and display it using the
-// typical hex notation..
+// This example demonstrates how to convert the compact "bits" in a block header
+// which represent the target difficulty to a big integer and display it using
+// the typical hex notation.
 func ExampleCompactToBig() {
 	// Convert the bits from block 300000 in the main block chain.
 	bits := uint32(419465580)
@@ -72,3 +73,22 @@ func ExampleCompactToBig() {
 	// Output:
 	// 0000000000000000896c00000000000000000000000000000000000000000000
 }
+
+// This example demonstrates how to convert a target difficulty into the compact
+// "bits" in a block header which represent that target difficulty .
+func ExampleBigToCompact() {
+	// Convert the target difficulty from block 300000 in the main block
+	// chain to compact form.
+	t := "0000000000000000896c00000000000000000000000000000000000000000000"
+	targetDifficulty, success := new(big.Int).SetString(t, 16)
+	if !success {
+		fmt.Println("invalid target difficulty")
+		return
+	}
+	bits := btcchain.BigToCompact(targetDifficulty)
+
+	fmt.Println(bits)
+
+	// Output:
+	// 419465580
+}