Mixed Signed and Unsigned Integers in Arithmetic Operations in GO

[etheleon]

Introduction

In the generated Go code from the Kaitai Struct (.ksy) definition, there is an arithmetic operation that mixes signed (int8) and unsigned (uint8) integers. Go does not allow such operations without explicit type conversion, resulting in a compilation error:

invalid operation: (this.Value1 + (this.Value2 << 8)) + (this.Value3 << 16) (mismatched types uint8 and int8)

.ksy definition

The .ksy definition of value is as follows:

  value:
    seq:
      - id: value1
        type: u1
      - id: value2
        type: u1
      - id: value3
        type: s1
    instances:
      calc_value:
        value: value1 + (value2 << 8) + (value3 << 16)

Generated Go Code

}
func (this *OpenapiMessage_Value) CalcValue() (v int, err error) {
	if this._f_calcValue {
		return this.calcValue, nil
	}
	this.calcValue = int(((this.Value1 + (this.Value2 << 8)) + (this.Value3 << 16)))
	this._f_calcValue = true
	return this.calcValue, nil
}

Proposed Fix

func (this *OpenapiMessage_Value) CalcValue() (v int, err error) {
    if this._f_calcValue {
        return this.calcValue, nil
    }

    // Convert values to appropriate types and perform arithmetic
    this.calcValue = int(
        int32(this.Value1) +          // value1 (u1 -> uint32)
        (int32(this.Value2) << 8) +  // value2 (u1 -> uint32, shifted left by 8 bits)
        (int32(this.Value3) << 16),   // value3 (s1 -> int32, shifted left by 16 bits)
    )

    this._f_calcValue = true
    return this.calcValue, nil
}

[etheleon]

if agreeable, i'll create the PR