dualfroz
dbeea4d2e3
MonomialEval started Horner evaluation from poly[len-2] instead of the highest-degree coefficient poly[len-1], so it silently ignored the top coefficient (1 + 2x at x=3 gave 1 instead of 7) and indexed poly[-1] on a constant polynomial, panicking. Start from poly[n] and iterate from n-1, matching the documented y = sum x^i * poly[i]. Closes #579
25 lines
869 B
Go
25 lines
869 B
Go
package bignum
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import (
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"math/big"
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"testing"
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"github.com/stretchr/testify/require"
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)
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func TestMonomialEval(t *testing.T) {
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newFloat := func(f float64) *big.Float { return new(big.Float).SetPrec(53).SetFloat64(f) }
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// 1 + 2x at x = 3 = 7: the highest-degree coefficient must not be dropped.
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got := MonomialEval(newFloat(3), []*big.Float{newFloat(1), newFloat(2)})
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require.Zerof(t, got.Cmp(newFloat(7)), "1 + 2x at x=3: got %v, want 7", got)
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// 1 + 2x + 3x^2 at x = 2 = 17.
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got = MonomialEval(newFloat(2), []*big.Float{newFloat(1), newFloat(2), newFloat(3)})
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require.Zerof(t, got.Cmp(newFloat(17)), "1 + 2x + 3x^2 at x=2: got %v, want 17", got)
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// A constant polynomial must return the constant without panicking.
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got = MonomialEval(newFloat(9), []*big.Float{newFloat(5)})
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require.Zerof(t, got.Cmp(newFloat(5)), "constant poly: got %v, want 5", got)
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}
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