From 917dbff89d30ce93c0853b7fc5cb1f25c498b4b5 Mon Sep 17 00:00:00 2001
From: Tobie Morgan Hitchcock <tobie@abcum.com>
Date: Fri, 13 Apr 2018 20:48:48 +0100
Subject: [PATCH] Add math.fixed function for truncating floats

---
 sql/funcs.go           | 1 +
 util/fncs/args.go      | 6 ++++++
 util/fncs/fnc.go       | 2 ++
 util/fncs/math.go      | 9 +++++++++
 util/fncs/math_test.go | 9 +++++++++
 5 files changed, 27 insertions(+)

diff --git a/sql/funcs.go b/sql/funcs.go
index 5af8f608..e3ff9967 100644
--- a/sql/funcs.go
+++ b/sql/funcs.go
@@ -123,6 +123,7 @@ var funcs = map[string]map[int]interface{}{
 	"math.ceil":          {1: nil},
 	"math.correlation":   {2: nil},
 	"math.covariance":    {2: nil},
+	"math.fixed":         {2: nil},
 	"math.floor":         {1: nil},
 	"math.geometricmean": {1: nil},
 	"math.harmonicmean":  {1: nil},
diff --git a/util/fncs/args.go b/util/fncs/args.go
index 715a8afd..0bb1423d 100644
--- a/util/fncs/args.go
+++ b/util/fncs/args.go
@@ -36,6 +36,12 @@ func outputFloat(val float64) (interface{}, error) {
 	}
 }
 
+func outputFixed(val float64, pre int64) (interface{}, error) {
+	out := math.Pow(10, float64(pre))
+	rnd := int(val*out + math.Copysign(0.5, val*out))
+	return float64(rnd) / out, nil
+}
+
 func ensureString(val interface{}) (out string, ok bool) {
 	switch val := val.(type) {
 	case string:
diff --git a/util/fncs/fnc.go b/util/fncs/fnc.go
index 7c52dddb..7ac2500e 100644
--- a/util/fncs/fnc.go
+++ b/util/fncs/fnc.go
@@ -116,6 +116,8 @@ func Run(ctx context.Context, name string, args ...interface{}) (interface{}, er
 		return mathCorrelation(ctx, args...)
 	case "math.covariance":
 		return mathCovariance(ctx, args...)
+	case "math.fixed":
+		return mathFixed(ctx, args...)
 	case "math.floor":
 		return mathFloor(ctx, args...)
 	case "math.geometricmean":
diff --git a/util/fncs/math.go b/util/fncs/math.go
index 4a676181..50322f41 100644
--- a/util/fncs/math.go
+++ b/util/fncs/math.go
@@ -54,6 +54,15 @@ func mathCovariance(ctx context.Context, args ...interface{}) (out interface{},
 	return outputFloat(math.Covariance(a, b))
 }
 
+func mathFixed(ctx context.Context, args ...interface{}) (out interface{}, err error) {
+	if val, ok := ensureFloat(args[0]); ok {
+		if pre, ok := ensureInt(args[1]); ok {
+			return outputFixed(val, pre)
+		}
+	}
+	return
+}
+
 func mathFloor(ctx context.Context, args ...interface{}) (out interface{}, err error) {
 	if val, ok := ensureFloat(args[0]); ok {
 		return outputFloat(math.Floor(val))
diff --git a/util/fncs/math_test.go b/util/fncs/math_test.go
index 9590c349..4f00e22a 100644
--- a/util/fncs/math_test.go
+++ b/util/fncs/math_test.go
@@ -80,6 +80,15 @@ func TestMath(t *testing.T) {
 		So(res, ShouldEqual, -1)
 	})
 
+	Convey("math.fixed() works properly", t, func() {
+		res, _ = Run(context.Background(), "math.fixed", "test")
+		So(res, ShouldEqual, nil)
+		res, _ = Run(context.Background(), "math.fixed", 10, 2)
+		So(res, ShouldEqual, 10)
+		res, _ = Run(context.Background(), "math.fixed", 1.51837461, 2)
+		So(res, ShouldEqual, 1.52)
+	})
+
 	Convey("math.floor() works properly", t, func() {
 		res, _ = Run(context.Background(), "math.floor", "test")
 		So(res, ShouldEqual, nil)