From 6fe2b4077896218083f778e926217f596a58a550 Mon Sep 17 00:00:00 2001
From: dweiller <4678790+dweiller@users.noreply.github.com>
Date: Sun, 10 Mar 2024 18:17:23 +1100
Subject: [PATCH] std.RingBuffer: use sliceAt/sliceFirst in read*AssumeLength

---
 lib/std/RingBuffer.zig | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/lib/std/RingBuffer.zig b/lib/std/RingBuffer.zig
index f47895ae5b..5bdfb3e070 100644
--- a/lib/std/RingBuffer.zig
+++ b/lib/std/RingBuffer.zig
@@ -150,12 +150,8 @@ pub fn readFirst(self: *RingBuffer, dest: []u8, length: usize) Error!void {
 /// Uses memcpy and so `dest` must not overlap ring buffer data.
 pub fn readFirstAssumeLength(self: *RingBuffer, dest: []u8, length: usize) void {
     assert(length <= self.len() and length <= dest.len);
-    const data_start = self.mask(self.read_index);
-    const part1_data_end = @min(self.data.len, data_start + length);
-    const part1_len = part1_data_end - data_start;
-    const part2_len = length - part1_len;
-    @memcpy(dest[0..part1_len], self.data[data_start..part1_data_end]);
-    @memcpy(dest[part1_len..length], self.data[0..part2_len]);
+    const slice = self.sliceAt(self.read_index, length);
+    slice.copyTo(dest);
     self.read_index = self.mask2(self.read_index + length);
 }
 
@@ -174,13 +170,12 @@ pub fn readLast(self: *RingBuffer, dest: []u8, length: usize) Error!void {
 /// Reduces write index by `length`.
 pub fn readLastAssumeLength(self: *RingBuffer, dest: []u8, length: usize) void {
     assert(length <= self.len() and length <= dest.len);
-    const data_start = self.mask(self.write_index + self.data.len - length);
-    const part1_data_end = @min(self.data.len, data_start + length);
-    const part1_len = part1_data_end - data_start;
-    const part2_len = length - part1_len;
-    @memcpy(dest[0..part1_len], self.data[data_start..part1_data_end]);
-    @memcpy(dest[part1_len..length], self.data[0..part2_len]);
-    self.write_index = if (self.write_index >= self.data.len) self.write_index - length else data_start;
+    const slice = self.sliceLast(length);
+    slice.copyTo(dest);
+    self.write_index = if (self.write_index >= self.data.len)
+        self.write_index - length
+    else
+        self.mask(self.write_index + self.data.len - length);
 }
 
 /// Returns `true` if the ring buffer is empty and `false` otherwise.
@@ -206,6 +201,12 @@ pub fn len(self: RingBuffer) usize {
 pub const Slice = struct {
     first: []u8,
     second: []u8,
+
+    /// Copy data from `self` into `dest`
+    pub fn copyTo(self: Slice, dest: []u8) void {
+        @memcpy(dest[0..self.first.len], self.first);
+        @memcpy(dest[self.first.len..][0..self.second.len], self.second);
+    }
 };
 
 /// Returns a `Slice` for the region of the ring buffer starting at