Created attachment 1294 [details]
Test caase

When I use std.BigInt to calculate the 939970th Fibonacci number, it works,
returning an integer with 196443 digits. However, when I try to calculate the
939971st Fibonacci number, I get an assertion failure in debug mode:

core.exception.AssertError@/home/demetri/bin/ldc/runtime/phobos/std/internal/math/biguintcore.d(1750):
Bigint Internal Error: Asymmetric Karatsuba

and a segfault in release mode. Stack trace:

#0  0x0000003c51b492e6 in __memcpy_ssse3_back () from /lib64/libc.so.6
#1  0x0000000000439ee8 in std.internal.math.biguintcore.inplaceSub() ()
#2  0x0000000000438b50 in std.internal.math.biguintcore.mulKaratsuba() ()
#3  0x0000000000438d29 in std.internal.math.biguintcore.mulKaratsuba() ()
#4  0x0000000000437544 in std.internal.math.biguintcore.mulInternal() ()
#5  0x0000000000436fff in std.internal.math.biguintcore.BigUint.mul() ()
#6  0x000000000040440a in
std.bigint.BigInt.__T8opBinaryVAyaa1_2aTS3std6bigint6BigIntZ.opBinary() ()
#7  0x0000000000404a65 in getints.fibonacci() ()
#8  0x0000000000403ad6 in getints.fibonacci() ()
#9  0x0000000000402f78 in D main ()
#10 0x00000000004586aa in rt.dmain2._d_run_main() ()
#11 0x00000000004582c6 in _d_run_main ()
#12 0x0000003c51a21b45 in __libc_start_main () from /lib64/libc.so.6
#13 0x0000000000402db9 in _start ()