diff options
Diffstat (limited to 'lib/pure/math.nim')
| -rw-r--r-- | lib/pure/math.nim | 29 |
1 files changed, 25 insertions, 4 deletions
diff --git a/lib/pure/math.nim b/lib/pure/math.nim index cbd04a145..9e590debc 100644 --- a/lib/pure/math.nim +++ b/lib/pure/math.nim @@ -29,11 +29,21 @@ proc binom*(n, k: int): int {.noSideEffect.} = for i in countup(2, k): result = (result * (n + 1 - i)) div i -proc fac*(n: int): int {.noSideEffect.} = +proc createFactTable[N: static[int]]: array[N, int] = + result[0] = 1 + for i in 1 ..< N: + result[i] = result[i - 1] * i + +proc fac*(n: int): int = ## Computes the faculty/factorial function. - result = 1 - for i in countup(2, n): - result = result * i + const factTable = + when sizeof(int) == 4: + createFactTable[13]() + else: + createFactTable[21]() + assert(n >= 0, $n & " must not be negative.") + assert(n < factTable.len, $n & " is too large to look up in the table") + factTable[n] {.push checks:off, line_dir:off, stack_trace:off.} @@ -550,3 +560,14 @@ when isMainModule: assert sgn(Inf) == 1 assert sgn(NaN) == 0 + block: # fac() tests + try: + discard fac(-1) + except AssertionError: + discard + + doAssert fac(0) == 1 + doAssert fac(1) == 1 + doAssert fac(2) == 2 + doAssert fac(3) == 6 + doAssert fac(4) == 24 |