faster digits(::BigInt) (JuliaLang#37075)

base/gmp.jl

@@ -10,7 +10,7 @@ import .Base: *, +, -, /, <, <<, >>, >>>, <=, ==, >, >=, ^, (~), (&), (|), xor,
  sum, trailing_zeros, trailing_ones, count_ones, tryparse_internal,
  bin, oct, dec, hex, isequal, invmod, _prevpow2, _nextpow2, ndigits0zpb,
  widen, signed, unsafe_trunc, trunc, iszero, isone, big, flipsign, signbit,
- sign, hastypemax, isodd
+ sign, hastypemax, isodd, digits!
 
 if Clong == Int32
  const ClongMax = Union{Int8, Int16, Int32}
@@ -694,6 +694,24 @@ function string(n::BigInt; base::Integer = 10, pad::Integer = 1)
  String(sv)
 end
 
+function digits!(a::AbstractVector{T}, n::BigInt; base::Integer = 10) where {T<:Integer}
+ if 2 ≤ base ≤ 62
+ s = codeunits(string(n; base))
+ i, j = firstindex(a)-1, length(s)+1
+ lasti = min(lastindex(a), firstindex(a) + length(s)-1 - isneg(n))
+ while i < lasti
+ # base ≤ 36: 0-9, plus a-z for 10-35
+ # base > 36: 0-9, plus A-Z for 10-35 and a-z for 36..61
+ x = s[j -= 1]
+ a[i += 1] = base ≤ 36 ? (x>0x39 ? x-0x57 : x-0x30) : (x>0x39 ? (x>0x60 ? x-0x3d : x-0x37) : x-0x30)
+ end
+ lasti = lastindex(a)
+ while i < lasti; a[i+=1] = zero(T); end
+ return isneg(n) ? map!(-,a,a) : a
+ end
+ return invoke(digits!, Tuple{typeof(a), Integer}, a, n; base) # slow generic fallback
+end
+
 function ndigits0zpb(x::BigInt, b::Integer)
  b < 2 && throw(DomainError(b, "`b` cannot be less than 2."))
  x.size == 0 && return 0 # for consistency with other ndigits0z methods

test/gmp.jl

@@ -293,6 +293,16 @@ let s, n = bigfib(1000001)
  @test startswith(s, "316047687386689")
 end
 
+@testset "digits" begin
+ n = Int64(2080310129088201558)
+ N = big(n)
+ for base in (2,7,10,11,16,30,50,62,64,100), pad in (0,1,10,100)
+ @test digits(n; base, pad) == digits(N; base, pad)
+ @test digits(-n; base, pad) == digits(-N; base, pad)
+ @test digits!(Vector{Int}(undef, pad), n; base) == digits!(Vector{Int}(undef, pad), N; base)
+ end
+end
+
 # serialization (#5133)
 let n = parse(BigInt, "359334085968622831041960188598043661065388726959079837"),
  b = IOBuffer()