overhaul mbsrtowcs

these changes fix at least two bugs:
- misaligned access to the input as uint32_t for vectorized ASCII test
- incorrect src pointer after stopping on EILSEQ

in addition, the text of the standard makes it unclear whether the
mbstate_t object is to be modified when the destination pointer is
null; previously it was cleared either way; now, it's only cleared
when the destination is non-null. this change may need revisiting, but
it should not affect most applications, since calling mbsrtowcs with
non-zero state can only happen when the head of the string was already
processed with mbrtowc.

finally, these changes shave about 20% size off the function and seem
to improve performance by 1-5%.

diff --git a/src/multibyte/mbsrtowcs.c b/src/multibyte/mbsrtowcs.c
index 8313d37..75a493c 100644 (file)
--- a/src/multibyte/mbsrtowcs.c
+++ b/src/multibyte/mbsrtowcs.c
@@ -13,93 +13,88 @@
 
 size_t mbsrtowcs(wchar_t *restrict ws, const char **restrict src, size_t wn, mbstate_t *restrict st)
 {
-       unsigned c;
        const unsigned char *s = (const void *)*src;
-       const wchar_t *wsorig = ws;
+       size_t wn0 = wn;
+       unsigned c = 0;
 
-       if (!st) st = (void *)&c, c = 0;
-       else c = *(unsigned *)st;
-
-       if (c) {
-               *(unsigned *)st = 0;
-               if (!ws) {
-                       wn = 0;
+       if (st && (c = *(unsigned *)st)) {
+               if (ws) {
+                       *(unsigned *)st = 0;
+                       goto resume;
+               } else {
                        goto resume0;
                }
-               goto resume;
        }
 
-       if (!ws) for (wn=0;;) {
-               if (*s-SA >= SB-SA) {
-                       while (((uintptr_t)s&3) && *s-1u<0x7f) s++, wn++;
-                       while (!(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) s+=4, wn+=4;
-                       while (*s-1u<0x7f) s++, wn++;
-                       if (!*s) return wn;
-                       if (*s-SA >= SB-SA) goto ilseq2;
+       if (!ws) for (;;) {
+               if (*s-1u < 0x7f && (uintptr_t)s%4 == 0) {
+                       while (!(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) {
+                               s += 4;
+                               wn -= 4;
+                       }
+               }
+               if (*s-1u < 0x7f) {
+                       s++;
+                       wn--;
+                       continue;
                }
+               if (*s-SA > SB-SA) break;
                c = bittab[*s++-SA];
-               do {
 resume0:
-                       if (OOB(c,*s)) goto ilseq2; s++;
-                       c <<= 6; if (!(c&(1U<<31))) break;
-                       if (*s++-0x80u >= 0x40) goto ilseq2;
-                       c <<= 6; if (!(c&(1U<<31))) break;
-                       if (*s++-0x80u >= 0x40) goto ilseq2;
-               } while (0);
-               wn++; c = 0;
-       }
-
-       while (wn) {
-               if (*s-SA >= SB-SA) {
-                       if (wn >= 7) {
-                               while (((uintptr_t)s&3) && *s-1u<0x7f) {
-                                       *ws++ = *s++;
-                                       wn--;
-                               }
-                               while (wn>=4 && !(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) {
-                                       *ws++ = *s++;
-                                       *ws++ = *s++;
-                                       *ws++ = *s++;
-                                       *ws++ = *s++;
-                                       wn -= 4;
-                               }
+               if (OOB(c,*s)) { s--; break; }
+               s++;
+               if (c&(1U<<25)) {
+                       if (*s-0x80u >= 0x40) { s-=2; break; }
+                       s++;
+                       if (c&(1U<<19)) {
+                               if (*s-0x80u >= 0x40) { s-=3; break; }
+                               s++;
                        }
-                       while (wn && *s-1u<0x7f) {
+               }
+               wn--;
+               c = 0;
+       } else for (;;) {
+               if (!wn) return wn0;
+               if (*s-1u < 0x7f && (uintptr_t)s%4 == 0) {
+                       while (wn>=4 && !(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) {
                                *ws++ = *s++;
-                               wn--;
-                       }
-                       if (!wn) break;
-                       if (!*s) {
-                               *ws = 0;
-                               *src = 0;
-                               return ws-wsorig;
+                               *ws++ = *s++;
+                               *ws++ = *s++;
+                               *ws++ = *s++;
+                               wn -= 4;
                        }
-                       if (*s-SA >= SB-SA) goto ilseq;
                }
+               if (*s-1u < 0x7f) {
+                       *ws++ = *s++;
+                       wn--;
+                       continue;
+               }
+               if (*s-SA > SB-SA) break;
                c = bittab[*s++-SA];
-               do {
 resume:
-                       if (OOB(c,*s)) goto ilseq;
-                       c = (c<<6) | *s++-0x80;
-                       if (!(c&(1U<<31))) break;
-
-                       if (*s-0x80u >= 0x40) goto ilseq;
-                       c = (c<<6) | *s++-0x80;
-                       if (!(c&(1U<<31))) break;
-
-                       if (*s-0x80u >= 0x40) goto ilseq;
+               if (OOB(c,*s)) { s--; break; }
+               c = (c<<6) | *s++-0x80;
+               if (c&(1U<<31)) {
+                       if (*s-0x80u >= 0x40) { s-=2; break; }
                        c = (c<<6) | *s++-0x80;
-               } while (0);
+                       if (c&(1U<<31)) {
+                               if (*s-0x80u >= 0x40) { s-=3; break; }
+                               c = (c<<6) | *s++-0x80;
+                       }
+               }
+               *ws++ = c;
+               wn--;
+               c = 0;
+       }
 
-               *ws++ = c; wn--; c = 0;
+       if (!c && !*s) {
+               if (ws) {
+                       *ws = 0;
+                       *src = 0;
+               }
+               return wn0-wn;
        }
-       *src = (const void *)s;
-       return ws-wsorig;
-ilseq:
-       *src = (const void *)s;
-ilseq2:
-       /* enter permanently failing state */
-       *(unsigned *)st = FAILSTATE;
        errno = EILSEQ;
+       if (ws) *src = (const void *)s;
        return -1;
 }