cmp(x, y: string) now uses memcmp rather than strcmp (#6869) (#6968)

lib/system.nim

@@ -2916,7 +2916,10 @@ when not defined(JS): #and not defined(nimscript):
       elif x > y: result = 1
       else: result = 0
     else:
-      result = int(c_strcmp(x, y))
+      let minlen = min(x.len, y.len)
+      result = int(c_memcmp(x.cstring, y.cstring, minlen.csize))
+      if result == 0:
+        result = x.len - y.len
 
   when defined(nimscript):
     proc readFile*(filename: string): string {.tags: [ReadIOEffect], benign.}

lib/system/sysstr.nim

@@ -24,10 +24,10 @@ proc cmpStrings(a, b: NimString): int {.inline, compilerProc.} =
   if a == b: return 0
   if a == nil: return -1
   if b == nil: return 1
-  when defined(nimNoArrayToCstringConversion):
-    return c_strcmp(addr a.data, addr b.data)
-  else:
-    return c_strcmp(a.data, b.data)
+  let minlen = min(a.len, b.len)
+  result = c_memcmp(addr a.data, addr b.data, minlen.csize)
+  if result == 0:
+    result = a.len - b.len
 
 proc eqStrings(a, b: NimString): bool {.inline, compilerProc.} =
   if a == b: return true

tests/stdlib/tstring.nim

@@ -56,4 +56,24 @@ proc test_string_slice() =
 
   echo("OK")
 
+proc test_string_cmp() =
+  let world = "hello\0world"
+  let earth = "hello\0earth"
+  let short = "hello\0"
+  let hello = "hello"
+  let goodbye = "goodbye"
+
+  doAssert world == world
+  doAssert world != earth
+  doAssert world != short
+  doAssert world != hello
+  doAssert world != goodbye
+
+  doAssert cmp(world, world) == 0
+  doAssert cmp(world, earth) > 0
+  doAssert cmp(world, short) > 0
+  doAssert cmp(world, hello) > 0
+  doAssert cmp(world, goodbye) > 0
+
 test_string_slice()
+test_string_cmp()