In config.setcpv() and regenerate(), replace str.startswith() calls with

slice comparison. It's not pretty but performance is critical in this section
of code and there is a measurable performance difference. (trunk r9896)

svn path=/main/branches/2.1.2/; revision=9897

diff --git a/pym/portage.py b/pym/portage.py
index 482ab8ff2a855be71f5a745bdafd69a3902be1fc..063acc5f75dbb8ee70a5dd8ebd8531e92fc596ba 100644 (file)
--- a/pym/portage.py
+++ b/pym/portage.py
@@ -2091,13 +2091,14 @@ class config:
                                        self.usemask.discard("test")
 
                # Use the calculated USE flags to regenerate the USE_EXPAND flags so
-               # that they are consistent.
+               # that they are consistent. For optimal performance, use slice
+               # comparison instead of startswith().
                use_expand = self.get("USE_EXPAND", "").split()
                for var in use_expand:
                        prefix = var.lower() + "_"
                        prefix_len = len(prefix)
                        expand_flags = set([ x[prefix_len:] for x in use \
-                               if x.startswith(prefix) ])
+                               if x[:prefix_len] == prefix ])
                        var_split = self.get(var, "").split()
                        # Preserve the order of var_split because it can matter for things
                        # like LINGUAS.
@@ -2108,13 +2109,13 @@ class config:
                                var_split = [ x for x in var_split if x != "*" ]
                        has_iuse = set()
                        for x in iuse_implicit:
-                               if x.startswith(prefix):
+                               if x[:prefix_len] == prefix:
                                        has_iuse.add(x[prefix_len:])
                        if has_wildcard:
                                # * means to enable everything in IUSE that's not masked
                                if has_iuse:
                                        for x in iuse_implicit:
-                                               if x.startswith(prefix) and x not in self.usemask:
+                                               if x[:prefix_len] == prefix and x not in self.usemask:
                                                        suffix = x[prefix_len:]
                                                        var_split.append(suffix)
                                                        use.add(x)
@@ -2450,6 +2451,8 @@ class config:
                                        self.uvlist.append(self.configdict[x])
                        self.uvlist.reverse()
 
+               # For optimal performance, use slice
+               # comparison instead of startswith().
                myflags = set()
                for curdb in self.uvlist:
                        cur_use_expand = [x for x in use_expand if x in curdb]
@@ -2479,8 +2482,9 @@ class config:
                                is_not_incremental = var not in myincrementals
                                if is_not_incremental:
                                        prefix = var_lower + "_"
+                                       prefix_len = len(prefix)
                                        for x in list(myflags):
-                                               if x.startswith(prefix):
+                                               if x[:prefix_len] == prefix:
                                                        myflags.remove(x)
                                for x in curdb[var].split():
                                        if x[0] == "+":