apd: avoid rapid b.StartTimer and b.StopTimer in benchmarks

They cause the benchmarks to run for a very long time.
See golang/go#27217.

Adjust the benchmarks to have an explicit setup phase
and run phase, separated by `b.ResetTimer`.

Author: nvanbenschoten

Diff for: gda_test.go

@@ -296,32 +296,43 @@ func (tc TestCase) Run(c *Context, done chan error, d, x, y *Decimal) (res Condi
 func BenchmarkGDA(b *testing.B) {
 	for _, fname := range GDAfiles {
 		b.Run(fname, func(b *testing.B) {
-			b.StopTimer()
+			type benchCase struct {
+				tc  TestCase
+				ctx *Context
+				res []Decimal
+				ops [2]*Decimal
+			}
 			_, tcs := readGDA(b, fname)
-			res := new(Decimal)
-			for i := 0; i < b.N; i++ {
-			Loop:
-				for _, tc := range tcs {
-					if GDAignore[tc.ID] || tc.Result == "?" || tc.HasNull() {
-						continue
-					}
-					switch tc.Operation {
-					case "apply", "toeng":
-						continue
-					}
-					operands := make([]*Decimal, 2)
-					for i, o := range tc.Operands {
-						d, _, err := NewFromString(o)
-						if err != nil {
-							continue Loop
-						}
-						operands[i] = d
+			bcs := make([]benchCase, 0, len(tcs))
+		Loop:
+			for _, tc := range tcs {
+				if GDAignore[tc.ID] || tc.Result == "?" || tc.HasNull() {
+					continue
+				}
+				switch tc.Operation {
+				case "apply", "toeng":
+					continue
+				}
+				bc := benchCase{
+					tc:  tc,
+					ctx: tc.Context(b),
+					res: make([]Decimal, b.N),
+				}
+				for i, o := range tc.Operands {
+					d, _, err := NewFromString(o)
+					if err != nil {
+						continue Loop
 					}
-					c := tc.Context(b)
-					b.StartTimer()
+					bc.ops[i] = d
+				}
+				bcs = append(bcs, bc)
+			}
+
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				for _, bc := range bcs {
 					// Ignore errors here because the full tests catch them.
-					_, _ = tc.Run(c, nil, res, operands[0], operands[1])
-					b.StopTimer()
+					_, _ = bc.tc.Run(bc.ctx, nil, &bc.res[i], bc.ops[0], bc.ops[1])
 				}
 			}
 		})

Diff for: table_test.go

@@ -23,44 +23,50 @@ import (
 )
 
 func BenchmarkNumDigitsLookup(b *testing.B) {
-	b.StopTimer()
-	runTest := func(start string, c byte) {
+	prep := func(start string, c byte) []*Decimal {
+		var ds []*Decimal
 		buf := bytes.NewBufferString(start)
 		for i := 1; i < digitsTableSize; i++ {
 			buf.WriteByte(c)
 			d, _, _ := NewFromString(buf.String())
-
-			b.StartTimer()
-			d.NumDigits()
-			b.StopTimer()
+			ds = append(ds, d)
 		}
+		return ds
 	}
+	var ds []*Decimal
+	ds = append(ds, prep("", '9')...)
+	ds = append(ds, prep("1", '0')...)
+	ds = append(ds, prep("-", '9')...)
+	ds = append(ds, prep("-1", '0')...)
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		runTest("", '9')
-		runTest("1", '0')
-		runTest("-", '9')
-		runTest("-1", '0')
+		for _, d := range ds {
+			d.NumDigits()
+		}
 	}
 }
 
 func BenchmarkNumDigitsFull(b *testing.B) {
-	b.StopTimer()
-	runTest := func(start string, c byte) {
+	prep := func(start string, c byte) []*Decimal {
+		var ds []*Decimal
 		buf := bytes.NewBufferString(start)
 		for i := 1; i < 1000; i++ {
 			buf.WriteByte(c)
 			d, _, _ := NewFromString(buf.String())
-
-			b.StartTimer()
-			d.NumDigits()
-			b.StopTimer()
+			ds = append(ds, d)
 		}
+		return ds
 	}
+	var ds []*Decimal
+	ds = append(ds, prep("", '9')...)
+	ds = append(ds, prep("1", '0')...)
+	ds = append(ds, prep("-", '9')...)
+	ds = append(ds, prep("-1", '0')...)
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		runTest("", '9')
-		runTest("1", '0')
-		runTest("-", '9')
-		runTest("-1", '0')
+		for _, d := range ds {
+			d.NumDigits()
+		}
 	}
 }