add nqp::div_In opcode

It smart-ish-ly divides two big integers and returns a double.

src/PAST/NQP.pir

@@ -450,6 +450,7 @@ entry to produce the node to be returned.
     maphash['mul_n']    = 'mul__Nnn'
     maphash['div_i']    = 'div__Iii'
     maphash['div_I']    = 'nqp_bigint_div__PPPP'
+    maphash['div_In']   = 'nqp_bigint_div_num__NPP'
     maphash['div_n']    = 'div__Nnn'
     maphash['mod_i']    = 'mod__Iii'
     maphash['mod_I']    = 'nqp_bigint_mod__PPPP'

src/ops/nqp_bigint.ops

@@ -304,6 +304,25 @@ inline op nqp_bigint_from_num(out PMC, in NUM, in PMC) :base_core {
     from_num($2, get_bigint(interp, $1));
 }
 
+inline op nqp_bigint_div_num(out NUM, in PMC, in PMC) :base_core {
+    mp_int *a = get_bigint(interp, $2);
+    mp_int *b = get_bigint(interp, $3);
+
+    int max_size = DIGIT_BIT * MAX(USED(a), USED(b));
+    if (max_size > 1023) {
+        mp_int reduced_a, reduced_b;
+        mp_init(&reduced_a);
+        mp_init(&reduced_b);
+        mp_div_2d(a, max_size - 1023, &reduced_a, NULL);
+        mp_div_2d(b, max_size - 1023, &reduced_b, NULL);
+        $1 = mp_get_double(&reduced_a) / mp_get_double(&reduced_b);
+        mp_clear(&reduced_a);
+        mp_clear(&reduced_b);
+    } else {
+        $1 = mp_get_double(a) / mp_get_double(b);
+    }
+}
+
 inline op nqp_bigint_shr(out PMC, in PMC, in INT, in PMC) :base_core {
     mp_int *a = get_bigint(interp, $2);
     $1 = REPR($4)->allocate(interp, STABLE($4));

t/nqp/60-bigint.t

@@ -1,7 +1,7 @@
 #! nqp
 use nqpmo;
 
-plan(32);
+plan(34);
 
 my $knowhow := pir::get_knowhow__P();
 my $bi_type := $knowhow.new_type(:name('TestBigInt'), :repr('P6bigint'));
@@ -93,3 +93,10 @@ ok(str(nqp::expmod_I(
     nqp::fromstr_I('10000000000000000000000000000000000000000', $bi_type),
     $bi_type,
 )) eq '1527229998585248450016808958343740453059', 'nqp::expmod_I');
+
+ok(nqp::div_In(box(1234500), box(100)) == 12345, 'div_In santiy');
+my $n := nqp::div_In(
+    nqp::pow_I(box(203), box(200), $bi_type, $bi_type),
+    nqp::pow_I(box(200), box(200), $bi_type, $bi_type),
+);
+ok(nqp::abs_n($n - 19.6430286394751) < 1e-10, 'div_In with big numbers');