master: arm64 utf8-strlen: test for null and non-ascii at the same time

The branch "master" has been updated in SBCL:
       via  b561a0680fb5988b86ca18a54a943c0247682f81 (commit)
      from  c68fdd2af1a169f4fb02e0e9fa45862a4c08851f (commit)

- Log -----------------------------------------------------------------
commit b561a0680fb5988b86ca18a54a943c0247682f81
Author: Stas Boukarev <[email protected]>
Date:   Mon Aug 10 07:06:34 2026 +0300

    arm64 utf8-strlen: test for null and non-ascii at the same time
---
 src/code/arm64-simd.lisp  |  8 ++++----
 src/code/x86-64-simd.lisp | 23 +++++++++--------------
 2 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/src/code/arm64-simd.lisp b/src/code/arm64-simd.lisp
index 489bdc747..54fb947b8 100644
--- a/src/code/arm64-simd.lisp
+++ b/src/code/arm64-simd.lisp
@@ -2050,10 +2050,10 @@
         (inst sub current current tmp1 :16b)
 
         ASCII
-        (inst uminv tmp1 current :16b)
-        (inst fmov tmp (reg-in-sc tmp1 'single-reg))
-        (inst cbz tmp ASCII-TAIL)
-        (check-ascii current tmp1 NON-ASCII :16b)
+        (inst sminv tmp1 current :16b)
+        (inst smov tmp tmp1 0 :b)
+        (inst cmp tmp 0) ;; either a null or a non-ascii character
+        (inst b :le ASCII-TAIL)
 
         (inst ldr current (@ ptr 16 :pre-index))
         (inst b ASCII)
diff --git a/src/code/x86-64-simd.lisp b/src/code/x86-64-simd.lisp
index 0421f684c..432c6fea4 100644
--- a/src/code/x86-64-simd.lisp
+++ b/src/code/x86-64-simd.lisp
@@ -2081,31 +2081,26 @@
 
         (inst vpxor zeros zeros zeros)
         ASCII
-        (inst vpcmpeqb tmp1 current zeros)
+        ;; If everything is greater than zero then it's ascii without a null
+        (inst vpcmpgtb tmp1 current zeros)
         (inst vpmovmskb tmp tmp1)
-        (inst test :dword tmp tmp)
+        (inst xor :dword tmp -1) ;; affects flags, unlike NOT
         (inst jmp :nz ASCII-TAIL)
 
-        (inst vpmovmskb tmp current)
-        (inst test :dword tmp tmp)
-        (inst jmp :nz NON-ASCII)
-
         (inst add ptr 32)
         (inst vmovdqa current (ea ptr))
         (inst jmp ASCII)
 
         ASCII-TAIL
-        (inst bsf :dword tmp tmp)
+        (inst vpmovmskb byte-length current) ;; non-ascii mask
 
-        (inst vpmovmskb byte-length current)
-        (inst test :dword byte-length byte-length)
-        (inst jmp :z ALL-ASCII-DONE)
+        (inst bsf :dword tmp tmp) ;; the first 0 or non-ascii bit
 
-        (inst bsf :dword byte-length byte-length)
-        (inst cmp :dword byte-length tmp)
-        (inst jmp :b NON-ASCII)
+        ;; If the first set bit is present in the non-ascii mask then
+        ;; the null-terminator is after it (or absent)
+        (inst bt :dword byte-length tmp)
+        (inst jmp :c NON-ASCII)
 
-        ALL-ASCII-DONE
         (inst add ptr tmp)
         (inst sub ptr bytes)
         (inst mov byte-length ptr)

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