1 files changed, 33 insertions, 0 deletions

diff --git a/src/ascii.zig b/src/ascii.zig
new file mode 100644
index 0000000..6c28f25
--- /dev/null
+++ b/src/ascii.zig
@@ -0,0 +1,33 @@
+const std = @import("std");
+const simd = std.simd;
+const testing = std.testing;
+
+/// Returns true if `str` only contains ASCII bytes. Uses SIMD if possible.
+pub fn isAsciiOnly(str: []const u8) bool {
+    const vec_len = simd.suggestVectorLength(u8) orelse return for (str) |b| {
+        if (b > 127) break false;
+    } else true;
+
+    const Vec = @Vector(vec_len, u8);
+    var remaining = str;
+
+    while (true) {
+        if (remaining.len < vec_len) return for (remaining) |b| {
+            if (b > 127) break false;
+        } else true;
+
+        const v1 = remaining[0..vec_len].*;
+        const v2: Vec = @splat(127);
+        if (@reduce(.Or, v1 > v2)) return false;
+        remaining = remaining[vec_len..];
+    }
+
+    return true;
+}
+
+test "isAsciiOnly" {
+    const ascii_only = "Hello, World! 0123456789 !@#$%^&*()_-=+";
+    try testing.expect(isAsciiOnly(ascii_only));
+    const not_ascii_only = "Héllo, World! 0123456789 !@#$%^&*()_-=+";
+    try testing.expect(!isAsciiOnly(not_ascii_only));
+}