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restore BCD functions as exported functions #58

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102 changes: 102 additions & 0 deletions decimal.go
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Original file line number Diff line number Diff line change
Expand Up @@ -530,6 +530,108 @@ func (d Decimal) String() string {
return string(buf[pos+1:])
}

// ParseBCD converts a [packed BCD] representation to a decimal.
//
// [packed BCD]: https://en.wikipedia.org/wiki/Binary-coded_decimal#Packed_BCD
func ParseBCD(b []byte) (Decimal, error) {
var pos int
width := len(b)

// Coefficient and sign
var neg bool
var coef fint
var ok bool
for pos < width {
hi := b[pos] >> 4
lo := b[pos] & 0x0f

if hi > 9 {
return Decimal{}, fmt.Errorf("%w: invalid high nibble \"%x\"", errInvalidDecimal, b[pos])
}
coef, ok = coef.fsa(1, hi)
if !ok {
return Decimal{}, errDecimalOverflow
}

if lo > 9 {
if lo == 0x0d {
neg = true
} else if lo != 0x0c {
return Decimal{}, fmt.Errorf("%w: invalid low nibble \"%x\"", errInvalidDecimal, b[pos])
}
pos++
break
}
coef, ok = coef.fsa(1, lo)
if !ok {
return Decimal{}, errDecimalOverflow
}
pos++
}

// Scale
var scale int
var hasScale bool
if pos < width {
hi := b[pos] >> 4
lo := b[pos] & 0x0f
hasScale = true

if hi > 1 {
return Decimal{}, fmt.Errorf("%w: invalid high nibble \"%x\"", errInvalidDecimal, b[pos])
}
scale = int(hi) * 10

if lo > 9 {
return Decimal{}, fmt.Errorf("%w: invalid low nibble \"%x\"", errInvalidDecimal, b[pos])
}
scale += int(lo)

pos++
}

if pos != width {
return Decimal{}, fmt.Errorf("%w: unexpected byte \"%x\"", errInvalidDecimal, b[pos])
}
if !hasScale {
return Decimal{}, fmt.Errorf("%w: no scale", errInvalidDecimal)
}

return newSafe(neg, coef, scale)
}

// BCD returns a [packed BCD] representation of a decimal.
//
// [packed BCD]: https://en.wikipedia.org/wiki/Binary-coded_decimal#Packed_BCD
func (d Decimal) BCD() []byte {
var buf [11]byte
pos := len(buf) - 1
coef := d.Coef()
scale := d.Scale()

// Scale
buf[pos] = byte(scale/10)<<4 | byte(scale%10)
pos--

// Sign and first digit
if d.IsNeg() {
buf[pos] = byte(coef%10)<<4 | 0x0d
} else {
buf[pos] = byte(coef%10)<<4 | 0x0c
}
pos--
coef /= 10

// Coefficient
for coef > 0 {
buf[pos] = byte(coef/10%10)<<4 | byte(coef%10)
pos--
coef /= 100
}

return buf[pos+1:]
}

// Float64 returns the nearest binary floating-point number rounded
// using [rounding half to even] (banker's rounding).
// See also constructor [NewFromFloat64].
Expand Down
131 changes: 131 additions & 0 deletions decimal_test.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package decimal

import (
"bytes"
"database/sql"
"database/sql/driver"
"encoding"
Expand Down Expand Up @@ -559,6 +560,136 @@ func TestDecimal_String(t *testing.T) {
})
}

func TestParseBCD(t *testing.T) {
t.Run("success", func(t *testing.T) {
tests := []struct {
bcd []byte
want string
}{
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x00}, "-9999999999999999999"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x01}, "-999999999999999999.9"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x02}, "-99999999999999999.99"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x03}, "-9999999999999999.999"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x19}, "-0.9999999999999999999"},
{[]byte{0x1d, 0x00}, "-1"},
{[]byte{0x1d, 0x01}, "-0.1"},
{[]byte{0x1d, 0x02}, "-0.01"},
{[]byte{0x1d, 0x19}, "-0.0000000000000000001"},
{[]byte{0x0c, 0x00}, "0"},
{[]byte{0x0c, 0x01}, "0.0"},
{[]byte{0x0c, 0x02}, "0.00"},
{[]byte{0x0c, 0x19}, "0.0000000000000000000"},
{[]byte{0x1c, 0x00}, "1"},
{[]byte{0x1c, 0x01}, "0.1"},
{[]byte{0x1c, 0x02}, "0.01"},
{[]byte{0x1c, 0x19}, "0.0000000000000000001"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x00}, "9999999999999999999"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x01}, "999999999999999999.9"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x02}, "99999999999999999.99"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x03}, "9999999999999999.999"},
{[]byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x19}, "0.9999999999999999999"},

// Exported constants
{[]byte{0x1d, 0x00}, NegOne.String()},
{[]byte{0x0c, 0x00}, Zero.String()},
{[]byte{0x1c, 0x00}, One.String()},
{[]byte{0x2c, 0x00}, Two.String()},
{[]byte{0x01, 0x0c, 0x00}, Ten.String()},
{[]byte{0x10, 0x0c, 0x00}, Hundred.String()},
{[]byte{0x01, 0x00, 0x0c, 0x00}, Thousand.String()},
{[]byte{0x27, 0x18, 0x28, 0x18, 0x28, 0x45, 0x90, 0x45, 0x23, 0x5c, 0x18}, E.String()},
{[]byte{0x31, 0x41, 0x59, 0x26, 0x53, 0x58, 0x97, 0x93, 0x23, 0x8c, 0x18}, Pi.String()},
}
for _, tt := range tests {
got, err := ParseBCD(tt.bcd)
if err != nil {
t.Errorf("parseBCD(% x) failed: %v", tt.bcd, err)
continue
}
want := MustParse(tt.want)
if got != want {
t.Errorf("parseBCD(% x) = %q, want %q", tt.bcd, got, want)
}
}
})

t.Run("error", func(t *testing.T) {
tests := map[string][]byte{
"empty": {},
"invalid nibble 1": {0x0f},
"invalid nibble 2": {0xf0},
"invalid nibble 3": {0x0c, 0x0f},
"invalid nibble 4": {0x0c, 0xf0},
"decimal overflow 1": {0x09, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x00},
"decimal overflow 2": {0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x00},
"no sign": {0x00},
"scale overflow": {0x0c, 0x00, 0x00},
}
for name, tt := range tests {
t.Run(name, func(t *testing.T) {
_, err := ParseBCD(tt)
if err == nil {
t.Errorf("parseBCD(% x) did not fail", tt)
}
})
}
})
}

func TestDecimal_BCD(t *testing.T) {
t.Run("success", func(t *testing.T) {
tests := []struct {
d string
want []byte
}{
{"-9999999999999999999", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x00}},
{"-999999999999999999.9", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x01}},
{"-99999999999999999.99", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x02}},
{"-9999999999999999.999", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x03}},
{"-0.9999999999999999999", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9d, 0x19}},
{"-1", []byte{0x1d, 0x00}},
{"-0.1", []byte{0x1d, 0x01}},
{"-0.01", []byte{0x1d, 0x02}},
{"-0.0000000000000000001", []byte{0x1d, 0x19}},
{"0", []byte{0x0c, 0x00}},
{"0.0", []byte{0x0c, 0x01}},
{"0.00", []byte{0x0c, 0x02}},
{"0.0000000000000000000", []byte{0x0c, 0x19}},
{"1", []byte{0x1c, 0x00}},
{"0.1", []byte{0x1c, 0x01}},
{"0.01", []byte{0x1c, 0x02}},
{"0.0000000000000000001", []byte{0x1c, 0x19}},
{"9999999999999999999", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x00}},
{"999999999999999999.9", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x01}},
{"99999999999999999.99", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x02}},
{"9999999999999999.999", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x03}},
{"0.9999999999999999999", []byte{0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9c, 0x19}},

// Exported constants
{NegOne.String(), []byte{0x1d, 0x00}},
{Zero.String(), []byte{0x0c, 0x00}},
{One.String(), []byte{0x1c, 0x00}},
{Two.String(), []byte{0x2c, 0x00}},
{Ten.String(), []byte{0x01, 0x0c, 0x00}},
{Hundred.String(), []byte{0x10, 0x0c, 0x00}},
{Thousand.String(), []byte{0x01, 0x00, 0x0c, 0x00}},
{E.String(), []byte{0x27, 0x18, 0x28, 0x18, 0x28, 0x45, 0x90, 0x45, 0x23, 0x5c, 0x18}},
{Pi.String(), []byte{0x31, 0x41, 0x59, 0x26, 0x53, 0x58, 0x97, 0x93, 0x23, 0x8c, 0x18}},
}
for _, tt := range tests {
d, err := Parse(tt.d)
if err != nil {
t.Errorf("Parse(%q) failed: %v", tt.d, err)
continue
}
got := d.BCD()
if !bytes.Equal(got, tt.want) {
t.Errorf("Parse(%q).bcd() = % x, want % x", tt.d, got, tt.want)
}
}
})
}

func TestDecimal_Float64(t *testing.T) {
tests := []struct {
d string
Expand Down