simd: add scalar fallbacks to all for build_options.simd false

src/build/Config.zig

@@ -460,6 +460,7 @@ pub fn addOptions(self: *const Config, step: *std.Build.Step.Options) !void {
     step.addOption(bool, "x11", self.x11);
     step.addOption(bool, "wayland", self.wayland);
     step.addOption(bool, "sentry", self.sentry);
+    step.addOption(bool, "simd", self.simd);
     step.addOption(bool, "i18n", self.i18n);
     step.addOption(ApprtRuntime, "app_runtime", self.app_runtime);
     step.addOption(FontBackend, "font_backend", self.font_backend);

src/build/SharedDeps.zig

@@ -112,6 +112,7 @@ pub fn add(
         const vt_options = @import("../terminal/build_options.zig");
         vt_options.addOptions(b, step.root_module, .{
             .artifact = .ghostty,
+            .simd = self.config.simd,
             .slow_runtime_safety = switch (optimize) {
                 .Debug => true,
                 .ReleaseSafe,

src/simd/base64.zig

@@ -1,4 +1,63 @@
 const std = @import("std");
+const options = @import("build_options");
+const assert = std.debug.assert;
+const log = std.log.scoped(.simd_base64);
+
+// Used for the non-SIMD implementation
+const Base64Decoder = std.base64.standard_no_pad.Decoder;
+
+pub fn maxLen(input: []const u8) usize {
+    if (comptime options.simd) return ghostty_simd_base64_max_length(
+        input.ptr,
+        input.len,
+    );
+
+    return maxLenScalar(input);
+}
+
+fn maxLenScalar(input: []const u8) usize {
+    return Base64Decoder.calcSizeForSlice(scalarInput(input)) catch |err| {
+        log.warn("failed to calculate base64 size for payload: {}", .{err});
+        return 0;
+    };
+}
+
+pub fn decode(input: []const u8, output: []u8) error{Base64Invalid}![]const u8 {
+    if (comptime options.simd) {
+        const res = ghostty_simd_base64_decode(
+            input.ptr,
+            input.len,
+            output.ptr,
+        );
+        if (res < 0) return error.Base64Invalid;
+        return output[0..@intCast(res)];
+    }
+
+    return decodeScalar(input, output);
+}
+
+fn decodeScalar(
+    input_raw: []const u8,
+    output: []u8,
+) error{Base64Invalid}![]const u8 {
+    const input = scalarInput(input_raw);
+    const size = maxLenScalar(input);
+    if (size == 0) return "";
+    assert(output.len >= size);
+    Base64Decoder.decode(
+        output,
+        scalarInput(input),
+    ) catch return error.Base64Invalid;
+    return output[0..size];
+}
+
+/// For non-SIMD enabled builds, we trim the padding from the end of the
+/// base64 input in order to get identical output with the SIMD version.
+fn scalarInput(input: []const u8) []const u8 {
+    var i: usize = 0;
+    while (input[input.len - i - 1] == '=') i += 1;
+    return input[0 .. input.len - i];
+}
 
 // base64.cpp
 extern "c" fn ghostty_simd_base64_max_length(
@@ -11,16 +70,6 @@ extern "c" fn ghostty_simd_base64_decode(
     output: [*]u8,
 ) isize;
 
-pub fn maxLen(input: []const u8) usize {
-    return ghostty_simd_base64_max_length(input.ptr, input.len);
-}
-
-pub fn decode(input: []const u8, output: []u8) error{Base64Invalid}![]const u8 {
-    const res = ghostty_simd_base64_decode(input.ptr, input.len, output.ptr);
-    if (res < 0) return error.Base64Invalid;
-    return output[0..@intCast(res)];
-}
-
 test "base64 maxLen" {
     const testing = std.testing;
     const len = maxLen("aGVsbG8gd29ybGQ=");

src/simd/codepoint_width.zig

@@ -1,11 +1,12 @@
 const std = @import("std");
+const options = @import("build_options");
 
 // vt.cpp
 extern "c" fn ghostty_simd_codepoint_width(u32) i8;
 
 pub fn codepointWidth(cp: u32) i8 {
-    //return @import("ziglyph").display_width.codePointWidth(@intCast(cp), .half);
-    return ghostty_simd_codepoint_width(cp);
+    if (comptime options.simd) return ghostty_simd_codepoint_width(cp);
+    return @import("ziglyph").display_width.codePointWidth(@intCast(cp), .half);
 }
 
 test "codepointWidth basic" {

src/simd/index_of.zig

@@ -1,5 +1,6 @@
 const std = @import("std");
 const builtin = @import("builtin");
+const options = @import("build_options");
 
 extern "c" fn ghostty_simd_index_of(
     needle: u8,
@@ -8,8 +9,16 @@ extern "c" fn ghostty_simd_index_of(
 ) usize;
 
 pub fn indexOf(input: []const u8, needle: u8) ?usize {
-    const result = ghostty_simd_index_of(needle, input.ptr, input.len);
-    return if (result == input.len) null else result;
+    if (comptime options.simd) {
+        const result = ghostty_simd_index_of(needle, input.ptr, input.len);
+        return if (result == input.len) null else result;
+    }
+
+    return indexOfScalar(input, needle);
+}
+
+fn indexOfScalar(input: []const u8, needle: u8) ?usize {
+    return std.mem.indexOfScalar(u8, input, needle);
 }
 
 test "indexOf" {

src/simd/main.zig

@@ -1,3 +1,6 @@
+//! SIMD-optimized routines. If `build_options.simd` is false, then the API
+//! still works but we fall back to pure Zig scalar implementations.
+
 const std = @import("std");
 
 const codepoint_width = @import("codepoint_width.zig");

src/simd/vt.zig

@@ -1,4 +1,7 @@
 const std = @import("std");
+const options = @import("build_options");
+const assert = std.debug.assert;
+const indexOf = @import("index_of.zig").indexOf;
 
 // vt.cpp
 extern "c" fn ghostty_simd_decode_utf8_until_control_seq(
@@ -17,15 +20,43 @@ pub fn utf8DecodeUntilControlSeq(
     input: []const u8,
     output: []u32,
 ) DecodeResult {
-    var decoded: usize = 0;
-    const consumed = ghostty_simd_decode_utf8_until_control_seq(
-        input.ptr,
-        input.len,
-        output.ptr,
-        &decoded,
-    );
+    assert(output.len >= input.len);
 
-    return .{ .consumed = consumed, .decoded = decoded };
+    if (comptime options.simd) {
+        var decoded: usize = 0;
+        const consumed = ghostty_simd_decode_utf8_until_control_seq(
+            input.ptr,
+            input.len,
+            output.ptr,
+            &decoded,
+        );
+
+        return .{ .consumed = consumed, .decoded = decoded };
+    }
+
+    return utf8DecodeUntilControlSeqScalar(input, output);
+}
+
+fn utf8DecodeUntilControlSeqScalar(
+    input: []const u8,
+    output: []u32,
+) DecodeResult {
+    // Find our escape
+    const idx = indexOf(input, 0x1B) orelse input.len;
+
+    // Copy up to the escape
+    const view = std.unicode.Utf8View.init(input[0..idx]) catch unreachable;
+    var it = view.iterator();
+    var i: usize = 0;
+    while (it.nextCodepoint()) |cp| {
+        output[i] = @intCast(cp);
+        i += 1;
+    }
+
+    return .{
+        .consumed = idx,
+        .decoded = i,
+    };
 }
 
 test "decode no escape" {