strings: optimization of repeat + repeat_string()

vlib/strings/strings.v

@@ -1,11 +0,0 @@
-module strings
-
-pub fn repeat(c byte, n int) string {
-	if n <= 0 {
-		return ''
-	}
-	mut arr := [c].repeat(n + 1)
-	arr[n] = `\0`
-	return string(arr,n)
-}
-

vlib/strings/strings_c.v

@@ -0,0 +1,34 @@
+module strings
+
+// strings.repeat - fill a string with `n` repetitions of the character `c`
+pub fn repeat(c byte, n int) string {
+	if n <= 0 {
+		return ''
+	}
+	mut bytes := &byte(0)
+	unsafe { bytes = malloc(n + 1) }
+	C.memset( bytes, c, n )
+	bytes[n] = `0`
+	return string( bytes, n )
+}
+
+// strings.repeat_string - gives you `n` repetitions of the substring `s`
+// NB: strings.repeat, that repeats a single byte, is between 2x
+// and 24x faster than strings.repeat_string called for a 1 char string.
+pub fn repeat_string(s string, n int) string {
+	if n <= 0 || s.len == 0 {
+		return ''
+	}
+	slen := s.len
+	blen := slen*n
+	mut bytes := &byte(0)
+	unsafe { bytes = malloc(blen + 1) }
+	for bi in 0..n {
+		bislen := bi*slen
+		for si in 0..slen {
+			bytes[bislen+si] = s[si]
+		}
+	}
+	bytes[blen] = `0`
+	return string( bytes, blen )
+}

vlib/strings/strings_js.v

@@ -0,0 +1,18 @@
+module strings
+
+pub fn repeat(c byte, n int) string {
+	if n <= 0 {
+		return ''
+	}
+	mut arr := [c].repeat(n + 1)
+	arr[n] = `\0`
+	return string(arr,n)
+}
+
+pub fn repeat_string(s string, n int) string {
+/*
+  // TODO: uncomment this. It is commented for now, so that `v doc strings` works
+	res := # s.repeat(n)
+	return res
+*/
+}

vlib/strings/strings_test.v

@@ -5,3 +5,10 @@ fn test_repeat() {
 	assert strings.repeat(`a`, 1) == 'a'
 	assert strings.repeat(`a`, 0) == ''
 }
+
+fn test_repeat_string() {
+	assert strings.repeat_string('abc', 3) == 'abcabcabc'
+	assert strings.repeat_string('abc', 1) == 'abc'
+	assert strings.repeat_string('abc', 0) == ''
+	assert strings.repeat_string('', 200) == ''
+}