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Use safe limit for toRational(float, int) (#7021)

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Current limit `high(int32)` is not safe for 32-bit platforms
and it will overflow (even when running its own test suite).
Similar behaviour would be when try to set limit to `high(int64)`
on 64-bit platforms.

This change selects safe maximum value based on platform
size of int. Safe maximum considered half of int size (for
backward compatiblity).
This commit is contained in:
Sergey Avseyev
2018-01-03 14:41:10 +03:00
committed by Andreas Rumpf
parent d5f539dc87
commit 8941f5bd9c
1 changed files with 8 additions and 3 deletions
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11
lib/pure/rationals.nim
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@@ -39,7 +39,7 @@ proc toRational*[T:SomeInteger](x: T): Rational[T] =
result.num = x
result.den = 1
proc toRational*(x: float, n: int = high(int32)): Rational[int] =
proc toRational*(x: float, n: int = high(int) shr (sizeof(int) div 2 * 8)): Rational[int] =
## Calculates the best rational numerator and denominator
## that approximates to `x`, where the denominator is
## smaller than `n` (default is the largest possible
@@ -323,8 +323,13 @@ when isMainModule:
assert abs(toFloat(y) - 0.4814814814814815) < 1.0e-7
assert toInt(z) == 0
assert toRational(0.98765432) == 2111111029 // 2137499919
assert toRational(PI) == 817696623 // 260280919
when sizeof(int) == 8:
assert toRational(0.98765432) == 2111111029 // 2137499919
assert toRational(PI) == 817696623 // 260280919
when sizeof(int) == 4:
assert toRational(0.98765432) == 80 // 81
assert toRational(PI) == 355 // 113
assert toRational(0.1) == 1 // 10
assert toRational(0.9) == 9 // 10