GC Error when use BigInt

[ethe]

Simple fibonacci function like this:

require "big_int"

def fib(n : Int32, ret1 : BigInt = BigInt.new("0"), ret2 : BigInt = BigInt.new("1"))
  if n == 0
    return ret1
  else
    return fib(n-1, ret2, ret1+ret2)
  end
end

puts fib(100000)

Got below Error:

Invalid memory access (signal 11) at address 0x7ffeaabdccf8
[4343989] *CallStack::print_backtrace:Int32 +117
[4334072] __crystal_sigfault_handler +56
[4447960] sigfault_handler +40
[139850285739280] ???
[4556322] GC_clear_stack_inner +11
[4556406] GC_clear_stack_inner +95 (9 times)
[4556559] GC_clear_stack +129
[4533012] GC_core_malloc +358
[4578165] GC_malloc +148
[4534821] GC_generic_or_special_malloc +72
[4535354] GC_realloc +484
[4328152] __crystal_realloc +8
[4346090] *GC::realloc<Pointer(Void), UInt64>:Pointer(Void) +10
[4335821] ~proc(Pointer(Void), UInt64, UInt64 -> Pointer(Void)) +13
[139850290158250] __gmpz_realloc +58
[139850290092705] __gmpz_add +913
[4447012] *BigInt#+<BigInt, BigInt>:BigInt +116
[4336233] *fib<Int32, BigInt, BigInt>:BigInt +105
[4336295] *fib<Int32, BigInt, BigInt>:BigInt +167 (87117 times)
[4336091] *fib<Int32>:BigInt +251
[4328066] ???
[4335609] main +41
[139850277526080] __libc_start_main +240
[4325193] _start +41
[0] ???

Use Crystal 0.15.0, LLVM 3.6.2.

BTW, do you think syntax like def fib(n : Int32, ret1 : BigInt = BigInt.new("0"), ret2 : BigInt = BigInt.new("1")) seems too looooong?

[asterite]

I think it's just a stack overflow. I also tried this in Ruby and get a stack overflow too:

def fib(n, ret1 = 0, ret2 = 1)
  if n == 0
    return ret1
  else
    return fib(n - 1, ret2, ret1 + ret2)
  end
end

puts fib(100000)

It has nothing to do with the GC because if you run it with GC_DONT_GC=1 ... you still get a crash. The stack mentions the GC because the GC call probably needs more stack levels and that's where the error happens.

I say we should close this and relate it to #271 (stack overflows should say "stack overflow" when such error happens).

[ethe]

@asterite Ok, but Ruby does not support Tail Call Optimization, so I'm not surprised get stack overflow, seems Crystal support it, fib(10000) is no problem.