tpl/math: Add log function

It might be very useful for building tag clouds.

diff --git a/docs/content/templates/functions.md b/docs/content/templates/functions.md
index 0c6968bd27f6f40256a124a3c8700878c816f1a3..99fb56d68346428418a6324010fb056590c0216f 100644 (file)
--- a/docs/content/templates/functions.md
+++ b/docs/content/templates/functions.md
@@ -432,6 +432,12 @@ favicon.ico: {{.Width}} x {{.Height}}
 <td><code>{{div 6 3}}</code> → 2</td>
 </tr>
 
+<tr>
+<td><code>math.Log</code></td>
+<td>Natural logarithm of one float.</td>
+<td><code>{{math.Log 1.0}}</code> → 0</td>
+</tr>
+
 <tr>
 <td><code>mod</code></td>
 <td>Modulus of two integers.</td>
@@ -714,7 +720,7 @@ e.g.
 
 * `{{ "this is a text" | truncate 10 " ..." }}` → `this is a ...`
 * `{{ "<em>Keep my HTML</em>" | safeHTML | truncate 10 }}` → `<em>Keep my …</em>`
-* `{{ "With [Markdown](#markdown) inside." | markdownify | truncate 10 }}` → `With <a href='#markdown'>Markdown …</a>`  
+* `{{ "With [Markdown](#markdown) inside." | markdownify | truncate 10 }}` → `With <a href='#markdown'>Markdown …</a>`
 
 ### split
 

diff --git a/tpl/math/init.go b/tpl/math/init.go
index 3faf0e3a68052f104a9df7ca58cd32d00229d27c..4d740c537c9e24af7d6b206ca8ac133b4ff33353 100644 (file)
--- a/tpl/math/init.go
+++ b/tpl/math/init.go
@@ -43,6 +43,13 @@ func init() {
                        },
                )
 
+               ns.AddMethodMapping(ctx.Log,
+                       nil,
+                       [][2]string{
+                               {"{{math.Log 1}}", "0"},
+                       },
+               )
+
                ns.AddMethodMapping(ctx.Mod,
                        []string{"mod"},
                        [][2]string{

diff --git a/tpl/math/math.go b/tpl/math/math.go
index 57e7baf12464145b0cd8950f7bab2c3838b729d1..303f029afade81876b1edf5bf4bd65f2de6138b7 100644 (file)
--- a/tpl/math/math.go
+++ b/tpl/math/math.go
@@ -15,7 +15,10 @@ package math
 
 import (
        "errors"
+       "math"
        "reflect"
+
+       "github.com/spf13/cast"
 )
 
 // New returns a new instance of the math-namespaced template functions.
@@ -34,6 +37,16 @@ func (ns *Namespace) Div(a, b interface{}) (interface{}, error) {
        return DoArithmetic(a, b, '/')
 }
 
+func (ns *Namespace) Log(a interface{}) (float64, error) {
+       af, err := cast.ToFloat64E(a)
+
+       if err != nil {
+               return 0, errors.New("Log operator can't be used with non integer or float value")
+       }
+
+       return math.Log(af), nil
+}
+
 // Mod returns a % b.
 func (ns *Namespace) Mod(a, b interface{}) (int64, error) {
        av := reflect.ValueOf(a)

diff --git a/tpl/math/math_test.go b/tpl/math/math_test.go
index 40bed553982b0950564f7f908e5e9d99a5b253b1..49ac053fd653748d03396c9554b07df084552972 100644 (file)
--- a/tpl/math/math_test.go
+++ b/tpl/math/math_test.go
@@ -15,6 +15,7 @@ package math
 
 import (
        "fmt"
+       "math"
        "testing"
 
        "github.com/stretchr/testify/assert"
@@ -142,6 +143,42 @@ func TestDoArithmetic(t *testing.T) {
        }
 }
 
+func TestLog(t *testing.T) {
+       t.Parallel()
+
+       ns := New()
+
+       for i, test := range []struct {
+               a      interface{}
+               expect interface{}
+       }{
+               {1, float64(0)},
+               {3, float64(1.0986)},
+               {0, float64(math.Inf(-1))},
+               {1.0, float64(0)},
+               {3.1, float64(1.1314)},
+               {"abc", false},
+       } {
+               errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+               result, err := ns.Log(test.a)
+
+               if b, ok := test.expect.(bool); ok && !b {
+                       require.Error(t, err, errMsg)
+                       continue
+               }
+
+               // we compare only 4 digits behind point if its a real float
+               // otherwise we usually get different float values on the last positions
+               if result != math.Inf(-1) {
+                       result = float64(int(result*10000)) / 10000
+               }
+
+               require.NoError(t, err, errMsg)
+               assert.Equal(t, test.expect, result, errMsg)
+       }
+}
+
 func TestMod(t *testing.T) {
        t.Parallel()