How Does Go Handle the Precision of Constants During Compilation and Runtime?

How Go Performs Arithmetic on Constants

Constants in Go represent exact values of arbitrary precision during compilation. However, when generating the final executable binary, constants must be converted to finite precision types.

Storage and Representation of Constants

Untyped constants do not occupy memory at runtime. They exist solely during compilation and are not present in the executable. The compiler derives the type of an untyped constant from its default type. For example, in the code snippet const Huge = 1e1000, the constant Huge is of type float64.

Implementation Restrictions

While the language specifies constant precision as arbitrary, implementations may apply limitations. However, certain minimum precision levels are guaranteed:

• Integer constants: 256 bits
• Floating-point constants: 256-bit mantissa, 32-bit signed exponent

Handling Arbitrary Precision at Compile Time

The compiler employs internal representations with limited precision to process constants with arbitrary precision. However, the spec dictates that all constant expressions must be evaluated exactly within the defined precision limits.

When Precision Limits are Reached

If overflow or loss of precision occurs during constant expression evaluation, the compiler will report an error. Values exceeding the limits of finite types cannot be represented in the executable.

Summary

At runtime, Go's predefined types offer limited precision for constants. Developers can utilize packages like math/big and go/constant to handle values with arbitrary precision. During compilation, constants have arbitrary precision, but compilers may impose limitations. Only the result of constant expressions need to be converted to finite precision.

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