From d60777002f23d7b681a3701b57a2e966875f2e61 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Thu, 5 Jun 2025 15:36:12 -0400
Subject: [PATCH] Function multiversioning for n_string2

---
 src/parser3.h | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/src/parser3.h b/src/parser3.h
index b987eb3..d78f6da 100644
--- a/src/parser3.h
+++ b/src/parser3.h
@@ -396,27 +396,26 @@ inline PRESERVE_NONE WeaselJsonStatus n_string(Parser3 *self, char *buf,
   MUSTTAIL return Parser3::keepGoing(self, buf, bufEnd);
 }
 
-inline PRESERVE_NONE WeaselJsonStatus n_string2(Parser3 *self, char *buf,
-                                                char *bufEnd) {
+template <class V>
+PRESERVE_NONE WeaselJsonStatus n_string2_impl(Parser3 *self, char *buf,
+                                              char *bufEnd) {
   const auto before = buf;
 
   // Advance buf to the first "non-normal" character
   for (;;) {
-    constexpr int kStride = 64;
-    if (bufEnd - buf < kStride) [[unlikely]] {
+    if (bufEnd - buf < V::lanes) [[unlikely]] {
       while (buf != bufEnd &&
              tables.stringByteMeaning[uint8_t(*buf)] == Tables::NORMAL) {
         ++buf;
       }
       break;
     }
-    using V = simd<int8_t, kStride>;
     auto v = V{(int8_t *)buf};
     int normal =
         (v != V::splat('"') & v != V::splat('\\') & v >= V::splat(0x20))
             .count_leading_nonzero_lanes();
     buf += normal;
-    if (normal < kStride) {
+    if (normal < V::lanes) {
       break;
     }
   }
@@ -485,6 +484,24 @@ inline PRESERVE_NONE WeaselJsonStatus n_string2(Parser3 *self, char *buf,
   }
 }
 
+template WeaselJsonStatus
+n_string2_impl<simd<int8_t, 64, sse::Simd_x86_SSE>>(Parser3 *, char *, char *);
+
+template __attribute__((target("avx2"))) WeaselJsonStatus
+n_string2_impl<simd<int8_t, 64, sse::Simd_x86_AVX2>>(Parser3 *, char *, char *);
+
+__attribute__((target("default"))) inline PRESERVE_NONE WeaselJsonStatus
+n_string2(Parser3 *self, char *buf, char *bufEnd) {
+  MUSTTAIL return n_string2_impl<simd<int8_t, 64, sse::Simd_x86_SSE>>(self, buf,
+                                                                      bufEnd);
+}
+
+__attribute__((target("avx2"))) inline PRESERVE_NONE WeaselJsonStatus
+n_string2(Parser3 *self, char *buf, char *bufEnd) {
+  MUSTTAIL return n_string2_impl<simd<int8_t, 64, sse::Simd_x86_AVX2>>(
+      self, buf, bufEnd);
+}
+
 inline PRESERVE_NONE WeaselJsonStatus n_string_following_escape(Parser3 *self,
                                                                 char *buf,
                                                                 char *bufEnd) {