Add support for (u)int type conversion overflow detection

Author: rwxe

README.md

@@ -1,6 +1,6 @@
 [![Build Status](https://travis-ci.org/JohnCGriffin/overflow.png)](https://travis-ci.org/JohnCGriffin/overflow)
 # overflow
-Check for integer overflow in Golang arithmetic.
+Check for integer overflow in Golang arithmetic and type conversion.
 ### Install
 ```
 go get github.com/johncgriffin/overflow
@@ -13,6 +13,7 @@ go generate
 ```
 ### Synopsis
 
+#### Arithmetic overflow detection
 ```
 package main
 
@@ -48,6 +49,34 @@ yields the output
 
 For (u)int types, provide (U)Add, (U)Sub, (U)Mul, (U)Div, (U)Quotient, etc.
 
+
+#### Type conversion overflow detection
+```
+func main() {
+	var i uint
+	for i = math.MaxInt - 5; i <= math.MaxInt+5; i++ {
+		ret, ok := overflow.UintToInt(i)
+		fmt.Printf("%v -> (%v,%v)\n",
+			i, ret, ok)
+	}
+}
+```
+yields the output
+```
+9223372036854775802 -> (9223372036854775802,true)
+9223372036854775803 -> (9223372036854775803,true)
+9223372036854775804 -> (9223372036854775804,true)
+9223372036854775805 -> (9223372036854775805,true)
+9223372036854775806 -> (9223372036854775806,true)
+9223372036854775807 -> (9223372036854775807,true)
+9223372036854775808 -> (-9223372036854775808,false)
+9223372036854775809 -> (-9223372036854775807,false)
+9223372036854775810 -> (-9223372036854775806,false)
+9223372036854775811 -> (-9223372036854775805,false)
+9223372036854775812 -> (-9223372036854775804,false)
+```
+Provide UintToInt, IntToUint, Uint64ToInt32, Int32ToUint64, etc.
+
 ### Stay calm and panic
 
 There's a good case to be made that a panic is an unidiomatic but proper response.  Iff you
@@ -80,4 +109,3 @@ SOFTWARE.
 
 
 
-

overflow.go

@@ -142,6 +142,28 @@ func UQuotient(a, b uint) (uint, uint, bool) {
 	return uint(uq32), uint(ur32), ok
 }
 
+// IntToUint converts an int value to uint.
+// returning a converted value and a bool value indicating whether the operation is safe.
+func IntToUint(x int) (uint, bool) {
+	if _is64Bit() {
+		y64, ok := Int64ToUint64(int64(x))
+		return uint(y64), ok
+	}
+	y32, ok := Int32ToUint32(int32(x))
+	return uint(y32), ok
+}
+
+// UintToInt converts an uint value to int.
+// returning a converted value and a bool value indicating whether the operation is safe.
+func UintToInt(x uint) (int, bool) {
+	if _is64Bit() {
+		y64, ok := Uint64ToInt64(uint64(x))
+		return int(y64), ok
+	}
+	y32, ok := Uint32ToInt32(uint32(x))
+	return int(y32), ok
+}
+
 /************* Panic versions for int ****************/
 
 // Addp returns the sum of two ints, panicking on overflow
@@ -215,3 +237,21 @@ func UDivp(a, b uint) uint {
 	}
 	return r
 }
+
+// IntToUintp converts an uint value to int, panicking on overflow.
+func IntToUintp(x int) uint {
+	r, ok := IntToUint(x)
+	if !ok {
+		panic("conversion failure")
+	}
+	return r
+}
+
+// UintToIntp converts an uint value to int, panicking on overflow.
+func UintToIntp(x uint) int {
+	r, ok := UintToInt(x)
+	if !ok {
+		panic("conversion failure")
+	}
+	return r
+}