Better sizehint for primes

base/primes.jl

@@ -78,12 +78,13 @@ primesmask(n::Integer) = n <= typemax(Int) ? primesmask(Int(n)) :
 
 function primes(lo::Int, hi::Int)
     lo ≤ hi || throw(ArgumentError("the condition lo ≤ hi must be met"))
+    lo = max(2, lo) # note: if now lo > hi, then hi < 7
     list = Int[]
     lo ≤ 2 ≤ hi && push!(list, 2)
     lo ≤ 3 ≤ hi && push!(list, 3)
     lo ≤ 5 ≤ hi && push!(list, 5)
-    hi < 7 && return list
-    sizehint!(list, floor(Int, hi / log(hi)))
+    hi < 7 && return list 
+    sizehint!(list, floor(Int, hi / log(hi) - lo / log(lo))) 
     sieve = _primesmask(max(7, lo), hi)
     lwi = wheel_index(lo - 1)
     @inbounds for i = 1:length(sieve)   # don't use eachindex here

test/numbers.jl

@@ -2253,6 +2253,9 @@ for T in [Int,BigInt], n = [1:1000;1000000]
         @test s[k] == primesmask(k, k)[1]
     end
 end
+let i = rand(1:2^(3*min(WORD_SIZE,64)÷4))
+    @test primes(i,i+1476) == filter(isprime, i:i + 1476) == filter(isprime, big(i:i + 1476))
+end
 
 @test !isprime(1000000003)
 @test !isprime(1000000005)