[i386/x86_64] Fix jsimd_encode_mcu_AC_first_prepare_sse2 when Sl is a…

… multiple of 16 (fixes libjpeg-turbo#335)

The SSE2 optimized version did extra iterations when
Sl was a multiple of 16.

CMakeLists.txt

@@ -720,6 +720,7 @@ if(WITH_12BIT)
   set(MD5_PPM_444_ISLOW_SKIP1_6 ef63901f71ef7a75cd78253fc0914f84)
   set(MD5_PPM_444_ISLOW_PROG_CROP98x98_13_13 15b173fb5872d9575572fbcc1b05956f)
   set(MD5_JPEG_CROP cdb35ff4b4519392690ea040c56ea99c)
+  set(MD5_JPEG_SCANS_16 d4d6e03300262fb294948daec71f6be4)
 else()
   set(TESTORIG testorig.jpg)
   set(MD5_JPEG_RGB_ISLOW 1d44a406f61da743b5fd31c0a9abdca3)
@@ -784,6 +785,7 @@ else()
   set(MD5_PPM_444_ISLOW_PROG_CROP98x98_13_13 db87dc7ce26bcdc7a6b56239ce2b9d6c)
   set(MD5_PPM_444_ISLOW_ARI_CROP37x37_0_0 cb57b32bd6d03e35432362f7bf184b6d)
   set(MD5_JPEG_CROP b4197f377e621c4e9b1d20471432610d)
+  set(MD5_JPEG_SCANS_16 bf1e87d7639f61186690ce912211d879)
 endif()
 
 if(WITH_JAVA)
@@ -1265,6 +1267,10 @@ foreach(libtype ${TEST_LIBTYPES})
     testout_crop.jpg ${TESTIMAGES}/${TESTORIG}
     ${MD5_JPEG_CROP})
 
+  add_bittest(jpegtran scans_16 "-copy;all;-scans;${TESTIMAGES}/test_scans_16.scan"
+    testout_scans_16.jpg ${TESTIMAGES}/${TESTORIG}
+    ${MD5_JPEG_SCANS_16})
+
 endforeach()
 
 add_custom_target(testclean COMMAND ${CMAKE_COMMAND} -P

simd/i386/jcphuff-sse2.asm

@@ -329,6 +329,8 @@ EXTN(jsimd_encode_mcu_AC_first_prepare_sse2):
     add         LUT, 16*SIZEOF_INT
     dec         K
     jnz         .BLOOP16
+    test        LEN, 15
+    je          .PADDING
 .ELOOP16:
     mov         LENEND, LEN
     and         LENEND, 7

simd/x86_64/jcphuff-sse2.asm

@@ -322,6 +322,8 @@ EXTN(jsimd_encode_mcu_AC_first_prepare_sse2):
     add         LUT, 16*SIZEOF_INT
     dec         K
     jnz         .BLOOP16
+    test        LEN, 15
+    je          .PADDING
 .ELOOP16:
     test        LEN, 8
     jz          .TRY7

testimages/test_scans_16.scan

@@ -0,0 +1,5 @@
+0 1 2: 0 0 0 0;
+0: 1 16 0 0;
+0: 17 63 0 0;
+1: 1 63 0 0;
+2: 1 63 0 0;