Implement rounding mode for Number#round (#10413)

crystal-lang · Feb 28, 2021 · b018f28 · b018f28
1 parent eef60c4
commit b018f28
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Showing 5 changed files with 327 additions and 16 deletions.
diff --git a/spec/std/number_spec.cr b/spec/std/number_spec.cr
@@ -53,13 +53,32 @@ describe "Number" do
       15.151.round.should eq(15)
     end
 
-    it "infinity" do
-      Float64::INFINITY.round.infinite?.should eq(1)
-      Float32::INFINITY.round.infinite?.should eq(1)
-      (-Float64::INFINITY).round.infinite?.should eq(-1)
-      (-Float32::INFINITY).round.infinite?.should eq(-1)
+    it "infinity Float64" do
+      Float64::INFINITY.round.should eq Float64::INFINITY
+      Float64::INFINITY.round(digits: 0).should eq Float64::INFINITY
+      Float64::INFINITY.round(digits: 3).should eq Float64::INFINITY
+      Float64::INFINITY.round(digits: -3).should eq Float64::INFINITY
+      (-Float64::INFINITY).round.should eq -Float64::INFINITY
+      (-Float64::INFINITY).round(digits: 0).should eq -Float64::INFINITY
+      (-Float64::INFINITY).round(digits: 3).should eq -Float64::INFINITY
+      (-Float64::INFINITY).round(digits: -3).should eq -Float64::INFINITY
     end
 
+    {% if compare_versions(Crystal::VERSION, "0.36.1") > 0 %}
+      it "infinity Float32" do
+        Float32::INFINITY.round.should eq Float32::INFINITY
+        Float32::INFINITY.round(digits: 0).should eq Float32::INFINITY
+        Float32::INFINITY.round(digits: 3).should eq Float32::INFINITY
+        Float32::INFINITY.round(digits: -3).should eq Float32::INFINITY
+        (-Float32::INFINITY).round.should eq -Float32::INFINITY
+        (-Float32::INFINITY).round(digits: 0).should eq -Float32::INFINITY
+        (-Float32::INFINITY).round(digits: 3).should eq -Float32::INFINITY
+        (-Float32::INFINITY).round(digits: -3).should eq -Float32::INFINITY
+      end
+    {% else %}
+      pending "infinity Float32"
+    {% end %}
+
     it "nan" do
       Float64::NAN.round.nan?.should be_true
       Float32::NAN.round.nan?.should be_true
@@ -116,6 +135,155 @@ describe "Number" do
       6543210987654321.0.round(-15).should eq(7000000000000000.0)
     end
 
+    describe "rounding modes" do
+      it "to_zero" do
+        -1.5.round(:to_zero).should eq -1.0
+        -1.0.round(:to_zero).should eq -1.0
+        -0.9.round(:to_zero).should eq 0.0
+        -0.5.round(:to_zero).should eq 0.0
+        -0.1.round(:to_zero).should eq 0.0
+        0.0.round(:to_zero).should eq 0.0
+        0.1.round(:to_zero).should eq 0.0
+        0.5.round(:to_zero).should eq 0.0
+        0.9.round(:to_zero).should eq 0.0
+        1.0.round(:to_zero).should eq 1.0
+        1.5.round(:to_zero).should eq 1.0
+      end
+
+      it "to_positive" do
+        -1.5.round(:to_positive).should eq -1.0
+        -1.0.round(:to_positive).should eq -1.0
+        -0.9.round(:to_positive).should eq 0.0
+        -0.5.round(:to_positive).should eq 0.0
+        -0.1.round(:to_positive).should eq 0.0
+        0.0.round(:to_positive).should eq 0.0
+        0.1.round(:to_positive).should eq 1.0
+        0.5.round(:to_positive).should eq 1.0
+        0.9.round(:to_positive).should eq 1.0
+        1.0.round(:to_positive).should eq 1.0
+        1.5.round(:to_positive).should eq 2.0
+      end
+
+      it "to_negative" do
+        -1.5.round(:to_negative).should eq -2.0
+        -1.0.round(:to_negative).should eq -1.0
+        -0.9.round(:to_negative).should eq -1.0
+        -0.5.round(:to_negative).should eq -1.0
+        -0.1.round(:to_negative).should eq -1.0
+        0.0.round(:to_negative).should eq 0.0
+        0.1.round(:to_negative).should eq 0.0
+        0.5.round(:to_negative).should eq 0.0
+        0.9.round(:to_negative).should eq 0.0
+        1.0.round(:to_negative).should eq 1.0
+        1.5.round(:to_negative).should eq 1.0
+      end
+
+      it "ties_even" do
+        -2.5.round(:ties_even).should eq -2.0
+        -1.5.round(:ties_even).should eq -2.0
+        -1.0.round(:ties_even).should eq -1.0
+        -0.9.round(:ties_even).should eq -1.0
+        -0.5.round(:ties_even).should eq 0.0
+        -0.1.round(:ties_even).should eq 0.0
+        0.0.round(:ties_even).should eq 0.0
+        0.1.round(:ties_even).should eq 0.0
+        0.5.round(:ties_even).should eq 0.0
+        0.9.round(:ties_even).should eq 1.0
+        1.0.round(:ties_even).should eq 1.0
+        1.5.round(:ties_even).should eq 2.0
+        2.5.round(:ties_even).should eq 2.0
+      end
+
+      it "ties_away" do
+        -2.5.round(:ties_away).should eq -3.0
+        -1.5.round(:ties_away).should eq -2.0
+        -1.0.round(:ties_away).should eq -1.0
+        -0.9.round(:ties_away).should eq -1.0
+        -0.5.round(:ties_away).should eq -1.0
+        -0.1.round(:ties_away).should eq 0.0
+        0.0.round(:ties_away).should eq 0.0
+        0.1.round(:ties_away).should eq 0.0
+        0.5.round(:ties_away).should eq 1.0
+        0.9.round(:ties_away).should eq 1.0
+        1.0.round(:ties_away).should eq 1.0
+        1.5.round(:ties_away).should eq 2.0
+        2.5.round(:ties_away).should eq 3.0
+      end
+
+      it "default (=ties_away)" do
+        -2.5.round.should eq -3.0
+        -1.5.round.should eq -2.0
+        -1.0.round.should eq -1.0
+        -0.9.round.should eq -1.0
+        -0.5.round.should eq -1.0
+        -0.1.round.should eq 0.0
+        0.0.round.should eq 0.0
+        0.1.round.should eq 0.0
+        0.5.round.should eq 1.0
+        0.9.round.should eq 1.0
+        1.0.round.should eq 1.0
+        1.5.round.should eq 2.0
+        2.5.round.should eq 3.0
+      end
+    end
+
+    describe "with digits" do
+      it "to_zero" do
+        12.345.round(-1, mode: :to_zero).should eq 10
+        12.345.round(0, mode: :to_zero).should eq 12
+        12.345.round(1, mode: :to_zero).should eq 12.3
+        12.345.round(2, mode: :to_zero).should eq 12.34
+        -12.345.round(-1, mode: :to_zero).should eq -10
+        -12.345.round(0, mode: :to_zero).should eq -12
+        -12.345.round(1, mode: :to_zero).should eq -12.3
+        -12.345.round(2, mode: :to_zero).should eq -12.34
+      end
+
+      it "to_positive" do
+        12.345.round(-1, mode: :to_positive).should eq 20
+        12.345.round(0, mode: :to_positive).should eq 13
+        12.345.round(1, mode: :to_positive).should eq 12.4
+        12.345.round(2, mode: :to_positive).should eq 12.35
+        -12.345.round(-1, mode: :to_positive).should eq -10
+        -12.345.round(0, mode: :to_positive).should eq -12
+        -12.345.round(1, mode: :to_positive).should eq -12.3
+        -12.345.round(2, mode: :to_positive).should eq -12.34
+      end
+
+      it "to_negative" do
+        12.345.round(-1, mode: :to_negative).should eq 10
+        12.345.round(0, mode: :to_negative).should eq 12
+        12.345.round(1, mode: :to_negative).should eq 12.3
+        12.345.round(2, mode: :to_negative).should eq 12.34
+        -12.345.round(-1, mode: :to_negative).should eq -20
+        -12.345.round(0, mode: :to_negative).should eq -13
+        -12.345.round(1, mode: :to_negative).should eq -12.4
+        -12.345.round(2, mode: :to_negative).should eq -12.35
+      end
+
+      it "ties_away" do
+        13.825.round(-1, mode: :ties_away).should eq 10
+        13.825.round(0, mode: :ties_away).should eq 14
+        13.825.round(1, mode: :ties_away).should eq 13.8
+        13.825.round(2, mode: :ties_away).should eq 13.83
+        -13.825.round(-1, mode: :ties_away).should eq -10
+        -13.825.round(0, mode: :ties_away).should eq -14
+        -13.825.round(1, mode: :ties_away).should eq -13.8
+        -13.825.round(2, mode: :ties_away).should eq -13.83
+      end
+
+      it "ties_even" do
+        15.255.round(-1, mode: :ties_even).should eq 20
+        15.255.round(0, mode: :ties_even).should eq 15
+        15.255.round(1, mode: :ties_even).should eq 15.3
+        15.255.round(2, mode: :ties_even).should eq 15.26
+        -15.255.round(-1, mode: :ties_even).should eq -20
+        -15.255.round(0, mode: :ties_even).should eq -15
+        -15.255.round(1, mode: :ties_even).should eq -15.3
+        -15.255.round(2, mode: :ties_even).should eq -15.26
+      end
+    end
+
     describe "base" do
       it "2" do
         -1763.116.round(2, base: 2).should eq(-1763.0)
@@ -132,6 +300,48 @@ describe "Number" do
     end
   end
 
+  describe "#round_even" do
+    -2.5.round_even.should eq -2.0
+    -1.5.round_even.should eq -2.0
+    -1.0.round_even.should eq -1.0
+    -0.9.round_even.should eq -1.0
+    -0.5.round_even.should eq -0.0
+    -0.1.round_even.should eq 0.0
+    0.0.round_even.should eq 0.0
+    0.1.round_even.should eq 0.0
+    0.5.round_even.should eq 0.0
+    0.9.round_even.should eq 1.0
+    1.0.round_even.should eq 1.0
+    1.5.round_even.should eq 2.0
+    2.5.round_even.should eq 2.0
+
+    1.round_even.should eq 1
+    1.round_even.should be_a(Int32)
+    1_u8.round_even.should be_a(UInt8)
+    1_f32.round_even.should be_a(Float32)
+  end
+
+  describe "#round_away" do
+    -2.5.round_away.should eq -3.0
+    -1.5.round_away.should eq -2.0
+    -1.0.round_away.should eq -1.0
+    -0.9.round_away.should eq -1.0
+    -0.5.round_away.should eq -1.0
+    -0.1.round_away.should eq 0.0
+    0.0.round_away.should eq 0.0
+    0.1.round_away.should eq 0.0
+    0.5.round_away.should eq 1.0
+    0.9.round_away.should eq 1.0
+    1.0.round_away.should eq 1.0
+    1.5.round_away.should eq 2.0
+    2.5.round_away.should eq 3.0
+
+    1.round_away.should eq 1
+    1.round_away.should be_a(Int32)
+    1_u8.round_away.should be_a(UInt8)
+    1_f32.round_away.should be_a(Float32)
+  end
+
   it "gives the absolute value" do
     123.abs.should eq(123)
     -123.abs.should eq(123)

diff --git a/src/float.cr b/src/float.cr
@@ -151,7 +151,21 @@ struct Float32
     LibM.floor_f32(self)
   end
 
-  def round
+  # Rounds towards the nearest integer. If both neighboring integers are equidistant,
+  # rounds towards the even neighbor (Banker's rounding).
+  def round_even : self
+    # LLVM 11 introduced llvm.roundeven.* intrinsics which may replace rint in
+    # the future.
+    {% if compare_versions(Crystal::LLVM_VERSION, "11.0.0") >= 0 %}
+      LibM.roundeven_f32(self)
+    {% else %}
+      LibM.rint_f32(self)
+    {% end %}
+  end
+
+  # Rounds towards the nearest integer. If both neighboring integers are equidistant,
+  # rounds away from zero.
+  def round_away
     LibM.round_f32(self)
   end
 
@@ -238,7 +252,21 @@ struct Float64
     LibM.floor_f64(self)
   end
 
-  def round
+  # Rounds towards the nearest integer. If both neighboring integers are equidistant,
+  # rounds towards the even neighbor (Banker's rounding).
+  def round_even : self
+    # LLVM 11 introduced llvm.roundeven.* intrinsics which may replace rint in
+    # the future.
+    {% if compare_versions(Crystal::LLVM_VERSION, "11.0.0") >= 0 %}
+      LibM.roundeven_f64(self)
+    {% else %}
+      LibM.rint_f64(self)
+    {% end %}
+  end
+
+  # Rounds towards the nearest integer. If both neighboring integers are equidistant,
+  # rounds away from zero.
+  def round_away
     LibM.round_f64(self)
   end
 

diff --git a/src/int.cr b/src/int.cr
@@ -241,6 +241,10 @@ struct Int
     self >= 0 ? self : -self
   end
 
+  def round(mode : RoundingMode) : self
+    self
+  end
+
   def ceil
     self
   end
@@ -249,11 +253,17 @@ struct Int
     self
   end
 
-  def round
+  def trunc
+    self
+  end
+
+  # Returns `self`.
+  def round_even : self
     self
   end
 
-  def trunc
+  # Returns `self`.
+  def round_away
     self
   end
 

diff --git a/src/math/libm.cr b/src/math/libm.cr
@@ -34,6 +34,12 @@ lib LibM
   {% end %}
   fun round_f32 = "llvm.round.f32"(value : Float32) : Float32
   fun round_f64 = "llvm.round.f64"(value : Float64) : Float64
+  {% if compare_versions(Crystal::LLVM_VERSION, "11.0.0") >= 0 %}
+    fun roundeven_f32 = "llvm.roundeven.f32"(value : Float32) : Float32
+    fun roundeven_f64 = "llvm.roundeven.f64"(value : Float64) : Float64
+  {% end %}
+  fun rint_f32 = "llvm.rint.f32"(value : Float32) : Float32
+  fun rint_f64 = "llvm.rint.f64"(value : Float64) : Float64
   fun sin_f32 = "llvm.sin.f32"(value : Float32) : Float32
   fun sin_f64 = "llvm.sin.f64"(value : Float64) : Float64
   fun sqrt_f32 = "llvm.sqrt.f32"(value : Float32) : Float32