logger: micro-optimize time stamping

Co-authored-by: Tony Chen <[email protected]>
Signed-off-by: Alex Aizman <[email protected]>

cmn/nlog/fixedbuf.go

@@ -8,6 +8,7 @@ package nlog
 import (
 	"io"
 	"os"
+	"time"
 )
 
 type fixed struct {
@@ -38,6 +39,50 @@ func (fb *fixed) writeByte(c byte) {
 	}
 }
 
+// "15:04:05.000000"
+func (fb *fixed) writeStamp() {
+	now := time.Now()
+	hour, minute, second := now.Clock()
+
+	fb.ab(hour)
+	fb.buf[fb.woff] = ':'
+	fb.woff++
+
+	fb.ab(minute)
+	fb.buf[fb.woff] = ':'
+	fb.woff++
+
+	fb.ab(second)
+	fb.buf[fb.woff] = '.'
+	fb.woff++
+
+	fb.abcdef(now.Nanosecond() / 1000)
+}
+
+const digits = "0123456789"
+
+func (fb *fixed) ab(d int) {
+	fb.buf[fb.woff] = digits[d/10]
+	fb.woff++
+
+	fb.buf[fb.woff] = digits[d%10]
+	fb.woff++
+}
+
+func (fb *fixed) abcdef(millis int) {
+	j := 5
+	for ; j >= 0 && millis > 0; j-- {
+		fb.buf[fb.woff+j] = digits[millis%10]
+		millis /= 10
+	}
+
+	const pad = '0'
+	for ; j >= 0; j-- {
+		fb.buf[fb.woff+j] = pad
+	}
+	fb.woff += 6
+}
+
 func (fb *fixed) flush(file *os.File) (n int, err error) {
 	n, err = file.Write(fb.buf[:fb.woff])
 	if err != nil {

cmn/nlog/nlog.go

@@ -275,8 +275,8 @@ func formatHdr(s severity, depth int, fb *fixed) {
 	}
 	fb.writeByte(char[s])
 	fb.writeByte(' ')
-	now := time.Now()
-	fb.writeString(now.Format("15:04:05.000000"))
+
+	fb.writeStamp()
 
 	fb.writeByte(' ')
 	if _, redact := redactFnames[fn]; redact {