h/fish-shell
1
Fork 0
mirror of https://github.com/fish-shell/fish-shell.git synced 2026-06-08 02:31:18 -03:00
Code Issues Packages Projects Releases Wiki Activity

Bypass recursion in case of single trailing nul in const_strlen()

Browse Source 
The default case for string literals like `"foo"` is a single trailing
nul, and that's what we have almost everywhere. By checking the
second-to-last index for a non-nul byte, we can skip the recursive
invocation, thus speeding up compilation that teeny, tinsy bit faster.
This commit is contained in:
Mahmoud Al-Qudsi
2021-02-17 12:22:32 -06:00
parent 071b9b13cd
commit 70b06a899d
1 changed files with 10 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
src/common.h
View File

@@ -733,14 +733,19 @@ static_assert(const_strcmp("b", "aa") > 0, "const_strcmp failure");
/// Compile-time agnostic-size strlen/wcslen implementation. Unicode-unaware.
template <typename T, size_t N>
constexpr size_t const_strlen(const T(&val)[N], ssize_t index = -1) {
// N is the length of the character array, but that includes one **or more** trailing nulls.
return index == -1 ? N - const_strlen(val, N - 1)
// N is the length of the character array, but that includes one **or more** trailing nuls.
static_assert(N > 0, "Invalid input to const_strlen");
return index == -1 ?
// Assume a minimum of one trailing nul and do a quick check for the usual case (single
// trailing nul) before recursing:
N - 1 - (N <= 2 || val[N-2] != static_cast<T>(0) ? 0 : const_strlen(val, N - 2))
// Prevent an underflow in case the string is comprised of all \0 bytes
: index == 0 ? 1
// Keep back-tracking until a non-null byte is found
: (val[index] == static_cast<T>(0) ? 1 + const_strlen(val, index - 1) : 0);
: index == 0 ? 0
// Keep back-tracking until a non-nul byte is found
: (val[index] != static_cast<T>(0) ? 0 : 1 + const_strlen(val, index - 1));
}
static_assert(const_strlen("") == 0, "const_strlen failure");
static_assert(const_strlen("a") == 1, "const_strlen failure");
static_assert(const_strlen("hello") == 5, "const_strlen failure");
/// Compile-time assertion of alphabetical sort of array `array`, by specified