strings: genSplit improvement #18973
Description
#go1.7, linux, amd64
The genSplit function used by Split, SplitAfter and SplitAfterN is simplified in the IF statement of sep length, maybe for code expression. However it results in extra conditional executions in either case of len(sep)==1 or len(sep)>1
if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
...
}
Just seperating that into two parts according to sep length gains ~15% improvement in performace (15% time reduction) in either case of len(sep)==1 or len(sep)>1.
func genSplit(s, sep string, sepSave, n int) []string {
if n == 0 {
return nil
}
if sep == "" {
return explode(s, n)
}
if n < 0 {
n = strings.Count(s, sep) + 1
}
c := sep[0]
start := 0
a := make([]string, n)
na := 0
if len(sep)==1 {
for i := 0; i < len(s) && na+1 < n; i++ {
if s[i] == c {
a[na] = s[start : i+sepSave]
na++
start = i + 1
}
}
} else {
for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
if s[i] == c && s[i:i+len(sep)] == sep {
a[na] = s[start : i+sepSave]
na++
start = i + len(sep)
i += len(sep) - 1
}
}
}
a[na] = s[start:]
return a[0 : na+1]
}