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Rewrite unescape_yaml to be faster and not needlessly trigger COW behavior of std::string

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This commit is contained in:
ridiculousfish 2013-04-07 14:59:48 -07:00
parent 42497d9932
commit 94acb6ed5d
1 changed files with 30 additions and 22 deletions
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52
history.cpp
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@ -657,7 +657,7 @@ static size_t trim_leading_spaces(std::string &str)
return i;
}
static bool extract_prefix(std::string &key, std::string &value, const std::string &line)
static bool extract_prefix_and_unescape_yaml(std::string &key, std::string &value, const std::string &line)
{
size_t where = line.find(":");
if (where != std::string::npos)
@ -689,7 +689,7 @@ history_item_t history_t::decode_item_fish_2_0(const char *base, size_t len)
/* Read the "- cmd:" line */
size_t advance = read_line(base, cursor, len, line);
trim_leading_spaces(line);
if (! extract_prefix(key, value, line) || key != "- cmd")
if (! extract_prefix_and_unescape_yaml(key, value, line) || key != "- cmd")
goto done;
cursor += advance;
@ -709,11 +709,10 @@ history_item_t history_t::decode_item_fish_2_0(const char *base, size_t len)
if (this_indent == 0 || indent != this_indent)
break;
if (! extract_prefix(key, value, line))
if (! extract_prefix_and_unescape_yaml(key, value, line))
break;
/* We are definitely going to consume this line */
unescape_yaml(value);
cursor += advance;
if (key == "when")
@ -1099,31 +1098,40 @@ static void escape_yaml(std::string &str)
replace_all(str, "\n", "\\n"); //replace newline with backslash + literal n
}
/* This function is called frequently, so it ought to be fast. */
static void unescape_yaml(std::string &str)
{
bool prev_escape = false;
for (size_t idx = 0; idx < str.size(); idx++)
size_t cursor = 0, size = str.size();
while (cursor < size)
{
char c = str.at(idx);
if (prev_escape)
// Operate on a const version of str, to avoid needless COWs that at() does.
const std::string &const_str = str;
// Look for a backslash
size_t backslash = const_str.find('\\', cursor);
if (backslash == std::string::npos || backslash + 1 >= size)
{
if (c == '\\')
{
/* Two backslashes in a row. Delete this one */
str.erase(idx, 1);
idx--;
}
else if (c == 'n')
{
/* Replace backslash + n with an actual newline */
str.replace(idx - 1, 2, "\n");
idx--;
}
prev_escape = false;
// Either not found, or found as the last character
break;
}
else
{
prev_escape = (c == '\\');
// Backslash found. Maybe we'll do something about it. Be sure to invoke the const version of at().
char escaped_char = const_str.at(backslash + 1);
if (escaped_char == '\\')
{
// Two backslashes in a row. Delete the second one.
str.erase(backslash + 1, 1);
size--;
}
else if (escaped_char == 'n')
{
// Backslash + n. Replace with a newline.
str.replace(backslash, 2, "\n");
size--;
}
// The character at index backslash has now been made whole; start at the next character
cursor = backslash + 1;
}
}
}