Initial data commit

Task/Currency/Go/currency.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+    "fmt"
+    "log"
+    "math/big"
+)
+
+// DC for dollars and cents.  Value is an integer number of cents.
+type DC int64
+
+func (dc DC) String() string {
+    d := dc / 100
+    if dc < 0 {
+        dc = -dc
+    }
+    return fmt.Sprintf("%d.%02d", d, dc%100)
+}
+
+// Extend returns extended price of a unit price.
+func (dc DC) Extend(n int) DC {
+    return dc * DC(n)
+}
+
+var one = big.NewInt(1)
+var hundred = big.NewRat(100, 1)
+
+// ParseDC parses dollars and cents as a string into a DC.
+func ParseDC(s string) (DC, bool) {
+    r, ok := new(big.Rat).SetString(s)
+    if !ok {
+        return 0, false
+    }
+    r.Mul(r, hundred)
+    if r.Denom().Cmp(one) != 0 {
+        return 0, false
+    }
+    return DC(r.Num().Int64()), true
+}
+
+// TR for tax rate.  Value is an an exact rational.
+type TR struct {
+    *big.Rat
+}
+func NewTR() TR {
+    return TR{new(big.Rat)}
+}
+
+// SetString overrides Rat.SetString to return the TR type.
+func (tr TR) SetString(s string) (TR, bool) {
+    if _, ok := tr.Rat.SetString(s); !ok {
+        return TR{}, false
+    }
+    return tr, true
+}
+
+var half = big.NewRat(1, 2)
+
+// Tax computes a tax amount, rounding to the nearest cent.
+func (tr TR) Tax(dc DC) DC {
+    r := big.NewRat(int64(dc), 1)
+    r.Add(r.Mul(r, tr.Rat), half)
+    return DC(new(big.Int).Div(r.Num(), r.Denom()).Int64())
+}
+
+func main() {
+    hamburgerPrice, ok := ParseDC("5.50")
+    if !ok {
+        log.Fatal("Invalid hamburger price")
+    }
+    milkshakePrice, ok := ParseDC("2.86")
+    if !ok {
+        log.Fatal("Invalid milkshake price")
+    }
+    taxRate, ok := NewTR().SetString("0.0765")
+    if !ok {
+        log.Fatal("Invalid tax rate")
+    }
+
+    totalBeforeTax := hamburgerPrice.Extend(4000000000000000) +
+        milkshakePrice.Extend(2)
+    tax := taxRate.Tax(totalBeforeTax)
+    total := totalBeforeTax + tax
+
+    fmt.Printf("Total before tax: %22s\n", totalBeforeTax)
+    fmt.Printf("             Tax: %22s\n", tax)
+    fmt.Printf("           Total: %22s\n", total)
+}