The Spec for Decimal Values

Oct 13, 2025 by wbrum.org 49 views

Introduction

The Advanced Message Queuing Protocol (AMQP) is a standard for message-oriented middleware that allows for the exchange of messages between applications. One of the key features of AMQP is its ability to handle decimal values, which are not floating-point values. In this article, we will explore the concept of decimal values in AMQP, their format, and how to handle unmarshalling and marshalling these values in Go.

What are Decimal Values?

Decimal values are a type of number that can be represented exactly as a finite decimal expansion. They are not floating-point values, which means they do not have a binary representation that can be subject to rounding errors. Decimal values are useful in financial and scientific applications where precision is critical.

AMQP and Decimal Values

AMQP allows for decimal values to be passed between applications. Some SDKs can handle these values, but Go does not have built-in support for decimal values. To properly support decimal values in Go, we need a binary marshaller/unmarshaller that can take the raw bytes and turn them into a proper type that is lossless.

The Spec for Decimal Values

The specification for decimal values and their format can be found on Wikipedia. The IEEE 754-2008 encoding standard defines the format for decimal values. The standard specifies that decimal values are represented as a sequence of bytes, with each byte representing a digit in the decimal expansion.

The Format of Decimal Values

The format of decimal values is as follows:

The first byte represents the sign of the decimal value (0 for positive, 1 for negative).
The next 4 bytes represent the exponent of the decimal value.
The remaining bytes represent the mantissa of the decimal value.

Unmarshalling Decimal Values in Go

Unmarshalling decimal values in Go involves taking the raw bytes and turning them into a proper type that is lossless. To do this, we need a binary marshaller/unmarshaller that can handle the raw bytes and turn them into a decimal value.

Marshalling Decimal Values in Go

Marshalling decimal values in Go involves taking a decimal value and turning it into raw bytes. To do this, we need a binary marshaller/unmarshaller that can handle the decimal value and turn it into raw bytes.

Implementing a Binary Marhsaller/Unmarshaller in Go

To implement a binary marshaller/unmarshaller in Go, we need to create a struct that can handle the raw bytes and turn them into a decimal value. We can use the encoding/binary package to help us with this.

Example Code

Here is an example of how we can implement a binary marshaller/unmarshaller in Go:

package main

import (
	"encoding/binary"
	"fmt"
)

// Decimal represents a decimal value
type Decimal struct {
	sign  uint8
	exponent uint32
	mantissa []byte
}

// NewDecimal returns a new decimal value
func NewDecimal(sign uint8, exponent uint32, mantissa []byte) *Decimal {
	return &Decimal{
		sign:  sign,
		exponent: exponent,
		mantissa: mantissa,
	}
}

// UnmarshalBinary unmarshals a decimal value from raw bytes
func (d *Decimal) UnmarshalBinary(data []byte) error {
	if len(data) < 5 {
		return fmt.Errorf("invalid decimal value")
	}

	d.sign = data[0]
	d.exponent = binary.BigEndian.Uint32(data[1:5])
	d.mantissa = data[5:]

	return nil
}

// MarshalBinary marshals a decimal value to raw bytes
func (d *Decimal) MarshalBinary() ([]byte, error) {
	data := make([]byte, 5+len(d.mantissa))
	data[0] = d.sign
	binary.BigEndian.PutUint32(data[1:5], d.exponent)
	copy(data[5:], d.mantissa)

	return data, nil
}

func main() {
	// Create a new decimal value
	d := NewDecimal(0, 123, []byte{1, 2, 3, 4, 5})

	// Unmarshal a decimal value from raw bytes
	data := []byte{0, 0, 0, 0, 123, 1, 2, 3, 4, 5}
	err := d.UnmarshalBinary(data)
	if err != nil {
		fmt.Println(err)
		return
	}

	// Marshal a decimal value to raw bytes
	data, err = d.MarshalBinary()
	if err != nil {
		fmt.Println(err)
		return
	}

	fmt.Println(data)
}

This code defines a Decimal struct that can handle the raw bytes and turn them into a decimal value. The UnmarshalBinary method unmarshals a decimal value from raw bytes, and the MarshalBinary method marshals a decimal value to raw bytes.

Conclusion

In this article, we explored the concept of decimal values in AMQP, their format, and how to handle unmarshalling and marshalling these values in Go. We implemented a binary marshaller/unmarshaller in Go using the encoding/binary package. This code can be used as a starting point for implementing decimal values in Go applications.

Future Work

In the future, we can improve the implementation of decimal values in Go by adding support for more decimal formats, such as the IEEE 754-2008 encoding standard. We can also improve the performance of the binary marshaller/unmarshaller by using more efficient algorithms.

References

Wikipedia: Decimal floating point
IEEE 754-2008 encoding standard
Handle Unmarshalling and Marshalling Decimal 32/64/128 Values: Q&A ====================================================================

Introduction

In our previous article, we explored the concept of decimal values in AMQP, their format, and how to handle unmarshalling and marshalling these values in Go. In this article, we will answer some frequently asked questions about handling decimal values in Go.

Q: What are decimal values in AMQP?

A: Decimal values in AMQP are a type of number that can be represented exactly as a finite decimal expansion. They are not floating-point values, which means they do not have a binary representation that can be subject to rounding errors.

Q: Why are decimal values important in AMQP?

A: Decimal values are important in AMQP because they provide a way to represent financial and scientific data exactly, without the risk of rounding errors. This is particularly important in applications such as financial trading, where small errors can have significant consequences.

Q: How do I handle decimal values in Go?

A: To handle decimal values in Go, you need to use a binary marshaller/unmarshaller that can take the raw bytes and turn them into a proper type that is lossless. You can use the encoding/binary package to help you with this.

Q: What is the format of decimal values in AMQP?

A: The format of decimal values in AMQP is defined by the IEEE 754-2008 encoding standard. The standard specifies that decimal values are represented as a sequence of bytes, with each byte representing a digit in the decimal expansion.

Q: How do I unmarshal a decimal value from raw bytes in Go?

A: To unmarshal a decimal value from raw bytes in Go, you need to use the UnmarshalBinary method of the Decimal struct. This method takes the raw bytes and turns them into a decimal value.

Q: How do I marshal a decimal value to raw bytes in Go?

A: To marshal a decimal value to raw bytes in Go, you need to use the MarshalBinary method of the Decimal struct. This method takes the decimal value and turns it into raw bytes.

Q: What are the benefits of using a binary marshaller/unmarshaller for decimal values in Go?

A: The benefits of using a binary marshaller/unmarshaller for decimal values in Go include:

Exact representation: Binary marshaller/unmarshallers can represent decimal values exactly, without the risk of rounding errors.
Efficient: Binary marshaller/unmarshallers are typically more efficient than other methods of handling decimal values.
Flexible: Binary marshaller/unmarshallers can handle a wide range of decimal formats, including the IEEE 754-2008 encoding standard.

Q: What are the challenges of using a binary marshaller/unmarshaller for decimal values in Go?

A: The challenges of using a binary marshaller/unmarshaller for decimal values in Go include:

Complexity: Binary marshaller/unmarshallers can be complex to implement and use.
Error handling: Binary marshaller/unmarshallers require careful error handling to ensure that decimal values are handled correctly.
Performance: Binary marshaller/unmarshallers can be slower than other methods of handling decimal values.

Conclusion

In this article, we answered some frequently asked questions about handling decimal values in Go. We discussed the importance of decimal values in AMQP, the format of decimal values, and how to handle unmarshalling and marshalling these values in Go. We also discussed the benefits and challenges of using a binary marshaller/unmarshaller for decimal values in Go.