Do not round a**b to infinity

... instead, just calculate the value unless it is too big.
Also, this change raises an ArgumentError if it is expected to exceed
16 GB in a 64-bit environment.

(It is possible to calculate it straightforward, but it would likely be
out-of-memory, so I didn't think it would make sense.)

[Feature #20811]

Author: mame

bignum.c

@@ -6287,8 +6287,7 @@ rb_big_pow(VALUE x, VALUE y)
         y = bignorm(y);
         if (FIXNUM_P(y))
             goto again;
-        rb_warn("in a**b, b may be too big");
-        d = rb_big2dbl(y);
+        rb_raise(rb_eArgError, "exponent is too large");
     }
     else if (FIXNUM_P(y)) {
         yy = FIX2LONG(y);
@@ -6304,13 +6303,16 @@ rb_big_pow(VALUE x, VALUE y)
             VALUE z = 0;
             SIGNED_VALUE mask;
             const size_t xbits = rb_absint_numwords(x, 1, NULL);
-            const size_t BIGLEN_LIMIT = 32*1024*1024;
+#if SIZEOF_SIZE_T == 4
+            const size_t BIGLEN_LIMIT = 1ULL << 31; // 2 GB
+#else // SIZEOF_SIZE_T == 8
+            const size_t BIGLEN_LIMIT = 1ULL << 34; // 16 GB
+#endif
 
             if (xbits == (size_t)-1 ||
                 (xbits > BIGLEN_LIMIT) ||
                 (xbits * yy > BIGLEN_LIMIT)) {
-                rb_warn("in a**b, b may be too big");
-                d = (double)yy;
+                rb_raise(rb_eArgError, "exponent is too large");
             }
             else {
                 for (mask = FIXNUM_MAX + 1; mask; mask >>= 1) {

rational.c

@@ -1048,8 +1048,7 @@ rb_rational_pow(VALUE self, VALUE other)
         }
     }
     else if (RB_BIGNUM_TYPE_P(other)) {
-        rb_warn("in a**b, b may be too big");
-        return rb_float_pow(nurat_to_f(self), other);
+        rb_raise(rb_eArgError, "exponent is too large");
     }
     else if (RB_FLOAT_TYPE_P(other) || RB_TYPE_P(other, T_RATIONAL)) {
         return rb_float_pow(nurat_to_f(self), other);

spec/ruby/core/integer/shared/exponent.rb

@@ -48,10 +48,18 @@
       (-1).send(@method, 4611686018427387905).should eql(-1)
     end
 
-    it "returns Float::INFINITY when the number is too big" do
-      -> {
-        2.send(@method, 427387904).should == Float::INFINITY
-      }.should complain(/warning: in a\*\*b, b may be too big/)
+    ruby_version_is ""..."3.4" do
+      it "returns Float::INFINITY when the number is too big" do
+        -> {
+          2.send(@method, 427387904).should == Float::INFINITY
+        }.should complain(/warning: in a\*\*b, b may be too big/)
+      end
+    end
+
+    ruby_version_is "3.4" do
+      it "raises an ArgumentError when the number is too big" do
+        -> { 100000000.send(@method, 1000000000) }.should raise_error(ArgumentError)
+      end
     end
 
     it "raises a ZeroDivisionError for 0 ** -1" do
@@ -108,13 +116,23 @@
       -> { @bignum.send(@method, :symbol) }.should raise_error(TypeError)
     end
 
-    it "switch to a Float when the values is too big" do
-      flt = nil
-      -> {
-        flt = @bignum.send(@method, @bignum)
-      }.should complain(/warning: in a\*\*b, b may be too big/)
-      flt.should be_kind_of(Float)
-      flt.infinite?.should == 1
+    ruby_version_is ""..."3.4" do
+      it "switch to a Float when the values is too big" do
+        flt = nil
+        -> {
+          flt = @bignum.send(@method, @bignum)
+        }.should complain(/warning: in a\*\*b, b may be too big/)
+        flt.should be_kind_of(Float)
+        flt.infinite?.should == 1
+      end
+    end
+
+    ruby_version_is "3.4" do
+      it "does not switch to a Float when the values is too big" do
+        -> {
+          @bignum.send(@method, @bignum)
+        }.should raise_error(ArgumentError)
+      end
     end
 
     it "returns a complex number when negative and raised to a fractional power" do

spec/ruby/shared/rational/exponent.rb

@@ -84,47 +84,91 @@
       (Rational(-1) ** bignum_value(3)).should eql(Rational(-1))
     end
 
-    it "returns positive Infinity when self is > 1" do
-      -> {
-        (Rational(2) ** bignum_value).infinite?.should == 1
-      }.should complain(/warning: in a\*\*b, b may be too big/)
-      -> {
-        (Rational(fixnum_max) ** bignum_value).infinite?.should == 1
-      }.should complain(/warning: in a\*\*b, b may be too big/)
-    end
-
-    it "returns 0.0 when self is > 1 and the exponent is negative" do
-      -> {
-        (Rational(2) ** -bignum_value).should eql(0.0)
-      }.should complain(/warning: in a\*\*b, b may be too big/)
-      -> {
-        (Rational(fixnum_max) ** -bignum_value).should eql(0.0)
-      }.should complain(/warning: in a\*\*b, b may be too big/)
-    end
-
-    # Fails on linux due to pow() bugs in glibc: http://sources.redhat.com/bugzilla/show_bug.cgi?id=3866
-    platform_is_not :linux do
-      it "returns positive Infinity when self < -1" do
+    ruby_version_is ""..."3.4" do
+      it "returns positive Infinity when self is > 1" do
         -> {
-          (Rational(-2) ** bignum_value).infinite?.should == 1
+          (Rational(2) ** bignum_value).infinite?.should == 1
         }.should complain(/warning: in a\*\*b, b may be too big/)
         -> {
-          (Rational(-2) ** (bignum_value + 1)).infinite?.should == 1
-        }.should complain(/warning: in a\*\*b, b may be too big/)
-        -> {
-          (Rational(fixnum_min) ** bignum_value).infinite?.should == 1
+          (Rational(fixnum_max) ** bignum_value).infinite?.should == 1
         }.should complain(/warning: in a\*\*b, b may be too big/)
       end
 
-      it "returns 0.0 when self is < -1 and the exponent is negative" do
+      it "returns 0.0 when self is > 1 and the exponent is negative" do
         -> {
-          (Rational(-2) ** -bignum_value).should eql(0.0)
+          (Rational(2) ** -bignum_value).should eql(0.0)
         }.should complain(/warning: in a\*\*b, b may be too big/)
         -> {
-          (Rational(fixnum_min) ** -bignum_value).should eql(0.0)
+          (Rational(fixnum_max) ** -bignum_value).should eql(0.0)
         }.should complain(/warning: in a\*\*b, b may be too big/)
       end
     end
+
+    ruby_version_is "3.4" do
+      it "raises an ArgumentError when self is > 1" do
+        -> {
+          (Rational(2) ** bignum_value)
+        }.should raise_error(ArgumentError)
+        -> {
+          (Rational(fixnum_max) ** bignum_value)
+        }.should raise_error(ArgumentError)
+      end
+
+      it "raises an ArgumentError when self is > 1 and the exponent is negative" do
+        -> {
+          (Rational(2) ** -bignum_value)
+        }.should raise_error(ArgumentError)
+        -> {
+          (Rational(fixnum_max) ** -bignum_value)
+        }.should raise_error(ArgumentError)
+      end
+    end
+
+    # Fails on linux due to pow() bugs in glibc: http://sources.redhat.com/bugzilla/show_bug.cgi?id=3866
+    platform_is_not :linux do
+      ruby_version_is ""..."3.4" do
+        it "returns positive Infinity when self < -1" do
+          -> {
+            (Rational(-2) ** bignum_value).infinite?.should == 1
+          }.should complain(/warning: in a\*\*b, b may be too big/)
+          -> {
+            (Rational(-2) ** (bignum_value + 1)).infinite?.should == 1
+          }.should complain(/warning: in a\*\*b, b may be too big/)
+          -> {
+            (Rational(fixnum_min) ** bignum_value).infinite?.should == 1
+          }.should complain(/warning: in a\*\*b, b may be too big/)
+        end
+
+        it "returns 0.0 when self is < -1 and the exponent is negative" do
+          -> {
+            (Rational(-2) ** -bignum_value).should eql(0.0)
+          }.should complain(/warning: in a\*\*b, b may be too big/)
+          -> {
+            (Rational(fixnum_min) ** -bignum_value).should eql(0.0)
+          }.should complain(/warning: in a\*\*b, b may be too big/)
+        end
+      end
+
+      ruby_version_is "3.4" do
+        it "returns positive Infinity when self < -1" do
+          -> {
+            (Rational(-2) ** bignum_value)
+          }.should raise_error(ArgumentError)
+          -> {
+            (Rational(fixnum_min) ** bignum_value)
+          }.should raise_error(ArgumentError)
+        end
+
+        it "returns 0.0 when self is < -1 and the exponent is negative" do
+          -> {
+            (Rational(-2) ** -bignum_value)
+          }.should raise_error(ArgumentError)
+          -> {
+            (Rational(fixnum_min) ** -bignum_value)
+          }.should raise_error(ArgumentError)
+        end
+      end
+    end
   end
 
   describe "when passed Float" do

test/ruby/test_bignum.rb

@@ -476,8 +476,8 @@ def test_quo
   def test_pow
     assert_equal(1.0, T32 ** 0.0)
     assert_equal(1.0 / T32, T32 ** -1)
-    assert_equal(1, assert_warning(/may be too big/) {T32 ** T32}.infinite?)
-    assert_equal(1, assert_warning(/may be too big/) {T32 ** (2**30-1)}.infinite?)
+    assert_raise(ArgumentError) { T32 ** T32 }
+    assert_raise(ArgumentError) { T32 ** (2**30-1) }
 
     ### rational changes the behavior of Bignum#**
     #assert_raise(TypeError) { T32**"foo" }

test/ruby/test_integer.rb

@@ -57,20 +57,19 @@ def test_pow
                           nil
                         end, "[ruby-dev:32084] [ruby-dev:34547]")
 
-    x = EnvUtil.suppress_warning {2 ** -0x4000000000000000}
-    assert_in_delta(0.0, (x / 2), Float::EPSILON)
+    assert_raise(ArgumentError) {2 ** -0x4000000000000000}
 
     <<~EXPRS.each_line.with_index(__LINE__+1) do |expr, line|
       crash01: 111r+11**-11111161111111
       crash02: 1118111111111**-1111111111111111**1+1==11111
-      crash03: -1111111**-1111*11 - -1111111** -111111111
+      crash03: -1111111**-1111*11 - -11** -11111111
       crash04: 1118111111111** -1111111111111111**1+11111111111**1 ===111
       crash05: 11** -111155555555555555  -55   !=5-555
       crash07: 1 + 111111111**-1111811111
       crash08: 18111111111**-1111111111111111**1 + 1111111111**-1111**1
       crash10: -7 - -1111111** -1111**11
       crash12: 1118111111111** -1111111111111111**1 + 1111 - -1111111** -1111*111111111119
-      crash13: 1.0i - -1111111** -111111111
+      crash13: 1.0i - -11** -11111111
       crash14: 11111**111111111**111111 * -11111111111111111111**-111111111111
       crash15: ~1**1111 + -~1**~1**111
       crash17: 11** -1111111**1111 /11i
@@ -80,7 +79,7 @@ def test_pow
       crash21: 11**-10111111119-1i -1r
     EXPRS
       name, expr = expr.split(':', 2)
-      assert_ruby_status(%w"-W0", expr, name)
+      assert_ruby_status(%w"-W0", "begin; #{ expr }; rescue ArgumentError; end", name)
     end
   end
 

test/ruby/test_rational.rb

@@ -1066,11 +1066,10 @@ def test_power_of_0
   end
 
   def test_power_overflow
-    bug = '[ruby-core:79686] [Bug #13242]: Infinity due to overflow'
-    x = EnvUtil.suppress_warning {4r**40000000}
-    assert_predicate x, :infinite?, bug
-    x = EnvUtil.suppress_warning {(1/4r)**40000000}
-    assert_equal 0, x, bug
+    assert_raise(ArgumentError) { 4r**400000000000000000000 }
+    exp = 4**40000000
+    assert_equal exp, 4r**40000000
+    assert_equal 1r/exp, (1/4r)**40000000
   end
 
   def test_positive_p