Why Do Go's Floating-Point Multiplication Results Differ When Using Literals versus Variables?

Why Does Floating-Point Multiplication Behave Differently with Literals vs. Variables in Go?

In Go, floating-point arithmetic exhibits a unique behavior when multiplying literals and variables. This anomaly arises due to the distinction between constants and variables in the language.

Constants and numeric literals, such as 10.1, have unlimited precision and are untyped. When assigned to a typed variable, they inherit the limitations of the assigned type. Thus, declaring x := 10.1 results in a float64 variable x with reduced precision.

In contrast, direct multiplication of literals, as in 10.1*3.0, operates on numbers with full precision. This difference in handling precision leads to the observed disparity in the comparison x*3.0 == 10.1*3.0.

This distinction is explained in the "Floats" section of the Go blog article "Constants." It notes that constants exist in an arbitrary-precision numeric space, but must conform to the destination type when assigned to a variable. While constants can represent very large or small values, they cannot be printed or assigned to variables without fitting within the target type's range.

Understanding this distinction is crucial for accurate floating-point calculations in Go. If absolute precision is required, it is recommended to use literals directly when performing arithmetic operations.

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