20 lines
552 B
Nim
20 lines
552 B
Nim
import posix, strutils
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proc `++`(a, b: float): tuple[lower, upper: float] =
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let
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a {.volatile.} = a
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b {.volatile.} = b
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orig = fegetround()
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discard fesetround FE_DOWNWARD
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result.lower = a + b
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discard fesetround FE_UPWARD
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result.upper = a + b
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discard fesetround orig
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proc ff(a: float): string = a.formatFloat(ffDefault, 17)
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for x, y in [(1.0, 2.0), (0.1, 0.2), (1e100, 1e-100), (1e308, 1e308)].items:
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let (d,u) = x ++ y
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echo x.ff, " + ", y.ff, " ="
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echo " [", d.ff, ", ", u.ff, "]"
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echo " size ", (u - d).ff, "\n"
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