88 lines
2.4 KiB
Go
88 lines
2.4 KiB
Go
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package calc
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import (
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"errors"
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"math"
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)
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// Base represents the current display formatting mode.
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type Base string
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const (
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BaseDEC Base = "DEC"
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BaseHEX Base = "HEX"
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BaseBIN Base = "BIN"
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BaseOCT Base = "OCT"
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)
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var basesCycle = []Base{BaseDEC, BaseHEX, BaseBIN, BaseOCT}
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// ErrConversionNotPossible is returned by CycleBase when the current value
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// has a fractional part and cannot be cleanly displayed in a non-DEC base.
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var ErrConversionNotPossible = errors.New("conversion not possible (CERR)")
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// Engine holds the calculator state. All math is decimal (float64).
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// Bases affect only formatting via FormatForDisplay and the small row.
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type Engine struct {
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value float64
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base Base
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pendingOp string // "+", "-", "*", "/", "mod", or ""
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pendingVal float64
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// entry buffer / more state will be added in engine implementation
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}
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// NewEngine creates a fresh calculator engine starting in DEC.
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func NewEngine() *Engine {
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return &Engine{
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value: 0,
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base: BaseDEC,
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}
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}
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// CurrentBase returns the active display base for the small row.
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func (e *Engine) CurrentBase() Base {
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return e.base
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}
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// IsInteger reports whether the current value is effectively an integer
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// (within epsilon to tolerate fp noise from operations like 1/3).
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func (e *Engine) IsInteger() bool {
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_, frac := math.Modf(e.value)
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return math.Abs(frac) < 1e-10
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}
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// CycleBase advances to the next base in the cycle (DEC→HEX→BIN→OCT→DEC).
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// Returns ErrConversionNotPossible (and does not change base) if the value
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// has a fractional part. The caller (UI) should trigger a "CERR" flash.
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func (e *Engine) CycleBase() error {
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if !e.IsInteger() {
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return ErrConversionNotPossible
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}
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for i, b := range basesCycle {
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if b == e.base {
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e.base = basesCycle[(i+1)%len(basesCycle)]
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return nil
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}
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}
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// fallback
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e.base = BaseDEC
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return nil
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}
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// FormatForDisplay returns the string to show in the large number area
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// according to the current base. For MVP only integer values are expected
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// in non-DEC bases (callers should have checked via CycleBase or IsInteger).
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func (e *Engine) FormatForDisplay() string {
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// Placeholder implementation. Real version in phase 2 will handle
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// proper integer formatting for hex/bin/oct (no 0x prefix, etc.)
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// and fall back gracefully.
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if e.base == BaseDEC {
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// simple for skeleton
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return "0"
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}
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return "0"
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}
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// TODO (phase 2): Add EnterDigit, SetOperator, Equals, Mod, ClearEntry,
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// AllClear, ChangeSign, Backspace, etc. + full FormatForDisplay.
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