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/**
This module contains compiler support for switch...case statements
Copyright: Copyright Digital Mars 2000 - 2019.
License: Distributed under the
$(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost Software License 1.0).
(See accompanying file LICENSE)
Source: $(DRUNTIMESRC core/internal/_switch_.d)
*/
module core.internal.switch_;
/**
Support for switch statements switching on strings.
Params:
caseLabels = sorted array of strings generated by compiler. Note the
strings are sorted by length first, and then lexicographically.
condition = string to look up in table
Returns:
index of match in caseLabels, a negative integer if not found
*/
int __switch(T, caseLabels...)(/*in*/ const scope T[] condition) pure nothrow @safe @nogc
{
// This closes recursion for other cases.
static if (caseLabels.length == 0)
{
return int.min;
}
else static if (caseLabels.length == 1)
{
return __cmp(condition, caseLabels[0]) == 0 ? 0 : int.min;
}
// To be adjusted after measurements
// Compile-time inlined binary search.
else static if (caseLabels.length < 7)
{
int r = void;
enum mid = cast(int)caseLabels.length / 2;
if (condition.length == caseLabels[mid].length)
{
r = __cmp(condition, caseLabels[mid]);
if (r == 0) return mid;
}
else
{
// Equivalent to (but faster than) condition.length > caseLabels[$ / 2].length ? 1 : -1
r = ((condition.length > caseLabels[mid].length) << 1) - 1;
}
if (r < 0)
{
// Search the left side
return __switch!(T, caseLabels[0 .. mid])(condition);
}
else
{
// Search the right side
return __switch!(T, caseLabels[mid + 1 .. $])(condition) + mid + 1;
}
}
else
{
// Need immutable array to be accessible in pure code, but case labels are
// currently coerced to the switch condition type (e.g. const(char)[]).
pure @trusted nothrow @nogc asImmutable(scope const(T[])[] items)
{
assert(__ctfe); // only @safe for CTFE
immutable T[][caseLabels.length] result = cast(immutable)(items[]);
return result;
}
static immutable T[][caseLabels.length] cases = asImmutable([caseLabels]);
// Run-time binary search in a static array of labels.
return __switchSearch!T(cases[], condition);
}
}
// binary search in sorted string cases, also see `__switch`.
private int __switchSearch(T)(/*in*/ const scope T[][] cases, /*in*/ const scope T[] condition) pure nothrow @safe @nogc
{
size_t low = 0;
size_t high = cases.length;
do
{
auto mid = (low + high) / 2;
int r = void;
if (condition.length == cases[mid].length)
{
r = __cmp(condition, cases[mid]);
if (r == 0) return cast(int) mid;
}
else
{
// Generates better code than "expr ? 1 : -1" on dmd and gdc, same with ldc
r = ((condition.length > cases[mid].length) << 1) - 1;
}
if (r > 0) low = mid + 1;
else high = mid;
}
while (low < high);
// Not found
return -1;
}
@system unittest
{
static void testSwitch(T)()
{
switch (cast(T[]) "c")
{
case "coo":
default:
break;
}
static int bug5381(immutable(T)[] s)
{
switch (s)
{
case "unittest": return 1;
case "D_Version2": return 2;
case "nonenone": return 3;
case "none": return 4;
case "all": return 5;
default: return 6;
}
}
int rc = bug5381("unittest");
assert(rc == 1);
rc = bug5381("D_Version2");
assert(rc == 2);
rc = bug5381("nonenone");
assert(rc == 3);
rc = bug5381("none");
assert(rc == 4);
rc = bug5381("all");
assert(rc == 5);
rc = bug5381("nonerandom");
assert(rc == 6);
static int binarySearch(immutable(T)[] s)
{
switch (s)
{
static foreach (i; 0 .. 16)
case i.stringof: return i;
default: return -1;
}
}
static foreach (i; 0 .. 16)
assert(binarySearch(i.stringof) == i);
assert(binarySearch("") == -1);
assert(binarySearch("sth.") == -1);
assert(binarySearch(null) == -1);
static int bug16739(immutable(T)[] s)
{
switch (s)
{
case "\u0100": return 1;
case "a": return 2;
default: return 3;
}
}
assert(bug16739("\u0100") == 1);
assert(bug16739("a") == 2);
assert(bug16739("foo") == 3);
}
testSwitch!char;
testSwitch!wchar;
testSwitch!dchar;
}
/**
Compiler lowers final switch default case to this (which is a runtime error)
Old implementation is in core/exception.d
*/
void __switch_error()(string file = __FILE__, size_t line = __LINE__)
{
import core.exception : __switch_errorT;
__switch_errorT(file, line);
}
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