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std: fix big int llshr to respect aliasing (#19612)

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Андрей Краевский 2024-04-13 13:06:23 +03:00 • committed by GitHub
parent 4fac5bd601
commit 7cc0e6d4cd
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2 changed files with 19 additions and 6 deletions
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12
lib/std/math/big/int.zig
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@ -3776,19 +3776,19 @@ fn llshr(r: []Limb, a: []const Limb, shift: usize) void {
const limb_shift = shift / limb_bits;
const interior_limb_shift = @as(Log2Limb, @truncate(shift));
var carry: Limb = 0;
var i: usize = 0;
while (i < a.len - limb_shift) : (i += 1) {
const src_i = a.len - i - 1;
const dst_i = src_i - limb_shift;
const dst_i = i;
const src_i = dst_i + limb_shift;
const src_digit = a[src_i];
r[dst_i] = carry | (src_digit >> interior_limb_shift);
carry = @call(.always_inline, math.shl, .{
const src_digit_next = if (src_i + 1 < a.len) a[src_i + 1] else 0;
const carry = @call(.always_inline, math.shl, .{
Limb,
src_digit,
src_digit_next,
limb_bits - @as(Limb, @intCast(interior_limb_shift)),
});
r[dst_i] = carry | (src_digit >> interior_limb_shift);
}
}

13
lib/std/math/big/int_test.zig
View file

@ -2019,6 +2019,19 @@ test "shift-right multi" {
try a.shiftRight(&a, 63);
try a.shiftRight(&a, 2);
try testing.expect(a.eqlZero());
try a.set(0xffff0000eeee1111dddd2222cccc3333000000000000000000000);
try a.shiftRight(&a, 84);
const string = try a.toString(
testing.allocator,
16,
.lower,
);
defer testing.allocator.free(string);
try std.testing.expectEqualStrings(
string,
"ffff0000eeee1111dddd2222cccc3333",
);
}
test "shift-left single" {