[GR-18163] Implement Integer.sqrt for large integers (#3872)

PullRequest: truffleruby/4539

Author: andrykonchin

CHANGELOG.md

@@ -25,6 +25,7 @@ Compatibility:
 * Fix `rb_str_locktmp()` and `rb_str_unlocktmp()` to raise `FrozenError` when string argument is frozen (#3752, @andrykonchin).
 * Fix Struct setters to raise `FrozenError` when a struct is frozen (#3850, @andrykonchin).
 * Fix `Struct#initialize` when mixed positional and keyword arguments (#3855, @andrykonchin).
+* Fix `Integer.sqrt` for large values (#3872, @tompng).
 
 Performance:
 

spec/tags/core/integer/sqrt_tags.txt

@@ -350,7 +350,17 @@ def self.try_convert(obj)
   def self.sqrt(n)
     n = Primitive.rb_to_int(n)
     raise Math::DomainError if n.negative?
-    Math.sqrt(n).floor
+    return Math.sqrt(n).floor if n < 0xfffffffffffff
+
+    shift = n.bit_length / 4
+    x = sqrt(n >> (2 * shift)) << shift
+    x = (x + n / x) / 2
+    xx = x * x
+    while xx > n
+      xx -= 2 * x - 1
+      x -= 1
+    end
+    x
   end
 
   private def upto_internal(val)

src/main/ruby/truffleruby/core/integer.rb

@@ -11,4 +11,3 @@
 exclude :test_floor, "<-100000000000000000000> expected but was <0>."
 exclude :test_pow, "FloatDomainError: Infinity"
 exclude :test_round, "<300> expected but was <200>."
-exclude :test_square_root, "10**33."