Integrate perlio:
[p5sagit/p5-mst-13.2.git] / toke.c
diff --git a/toke.c b/toke.c
index ea0f650..424249f 100644 (file)
--- a/toke.c
+++ b/toke.c
@@ -36,8 +36,12 @@ static I32 utf16rev_textfilter(pTHXo_ int idx, SV *sv, int maxlen);
 #define XFAKEBRACK 128
 #define XENUMMASK 127
 
-/*#define UTF (SvUTF8(PL_linestr) && !(PL_hints & HINT_BYTE))*/
-#define UTF ((PL_linestr && DO_UTF8(PL_linestr)) || PL_hints & HINT_UTF8)
+#ifdef EBCDIC
+/* For now 'use utf8' does not affect tokenizer on EBCDIC */
+#define UTF (PL_linestr && DO_UTF8(PL_linestr))
+#else
+#define UTF ((PL_linestr && DO_UTF8(PL_linestr)) || (PL_hints & HINT_UTF8))
+#endif
 
 /* In variables name $^X, these are the legal values for X.
  * 1999-02-27 mjd-perl-patch@plover.com */
@@ -177,13 +181,15 @@ int yyactlevel = -1;
 /* grandfather return to old style */
 #define OLDLOP(f) return(yylval.ival=f,PL_expect = XTERM,PL_bufptr = s,(int)LSTOP)
 
+#ifdef DEBUGGING
+
 STATIC void
 S_tokereport(pTHX_ char *thing, char* s, I32 rv)
 {
-    SV *report;
     DEBUG_T({
-        report = newSVpv(thing, 0);
-        Perl_sv_catpvf(aTHX_ report, ":line %i:%i:", CopLINE(PL_curcop), rv);
+        SV* report = newSVpv(thing, 0);
+        Perl_sv_catpvf(aTHX_ report, ":line %d:%"IVdf":", CopLINE(PL_curcop),
+               (IV)rv);
 
         if (s - PL_bufptr > 0)
             sv_catpvn(report, PL_bufptr, s - PL_bufptr);
@@ -192,9 +198,11 @@ S_tokereport(pTHX_ char *thing, char* s, I32 rv)
                 sv_catpv(report, PL_tokenbuf);
         }
         PerlIO_printf(Perl_debug_log, "### %s\n", SvPV_nolen(report));
-    })
+    });
 }
 
+#endif
+
 /*
  * S_ao
  *
@@ -533,7 +541,7 @@ S_skipspace(pTHX_ register char *s)
     for (;;) {
        STRLEN prevlen;
        SSize_t oldprevlen, oldoldprevlen;
-       SSize_t oldloplen, oldunilen;
+       SSize_t oldloplen = 0, oldunilen = 0;
        while (s < PL_bufend && isSPACE(*s)) {
            if (*s++ == '\n' && PL_in_eval && !PL_rsfp)
                incline(s);
@@ -1038,6 +1046,7 @@ S_sublex_push(pTHX)
     SAVEI32(PL_lex_inwhat);
     SAVECOPLINE(PL_curcop);
     SAVEPPTR(PL_bufptr);
+    SAVEPPTR(PL_bufend);
     SAVEPPTR(PL_oldbufptr);
     SAVEPPTR(PL_oldoldbufptr);
     SAVEPPTR(PL_last_lop);
@@ -1218,22 +1227,22 @@ S_scan_const(pTHX_ char *start)
     register char *d = SvPVX(sv);              /* destination for copies */
     bool dorange = FALSE;                      /* are we in a translit range? */
     bool didrange = FALSE;                     /* did we just finish a range? */
-    bool has_utf8 = (PL_linestr && SvUTF8(PL_linestr));
-                                               /* the constant is UTF8 */
+    I32  has_utf8 = FALSE;                     /* Output constant is UTF8 */
+    I32  this_utf8 = UTF;                      /* The source string is assumed to be UTF8 */
     UV uv;
 
-    I32 utf = (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op)
-       ? (PL_sublex_info.sub_op->op_private & (OPpTRANS_FROM_UTF|OPpTRANS_TO_UTF))
-       : UTF;
-    I32 this_utf8 = (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op)
-       ? (PL_sublex_info.sub_op->op_private & (PL_lex_repl ?
-                                               OPpTRANS_FROM_UTF : OPpTRANS_TO_UTF))
-       : UTF;
     const char *leaveit =      /* set of acceptably-backslashed characters */
        PL_lex_inpat
            ? "\\.^$@AGZdDwWsSbBpPXC+*?|()-nrtfeaxcz0123456789[{]} \t\n\r\f\v#"
            : "";
 
+    if (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op) {
+       /* If we are doing a trans and we know we want UTF8 set expectation */
+       has_utf8   = PL_sublex_info.sub_op->op_private & (OPpTRANS_FROM_UTF|OPpTRANS_TO_UTF);
+       this_utf8  = PL_sublex_info.sub_op->op_private & (PL_lex_repl ? OPpTRANS_FROM_UTF : OPpTRANS_TO_UTF);
+    }
+
+
     while (s < send || dorange) {
         /* get transliterations out of the way (they're most literal) */
        if (PL_lex_inwhat == OP_TRANS) {
@@ -1243,17 +1252,18 @@ S_scan_const(pTHX_ char *start)
                I32 min;                        /* first character in range */
                I32 max;                        /* last character in range */
 
-               if (utf) {
+               if (has_utf8) {
                    char *c = (char*)utf8_hop((U8*)d, -1);
                    char *e = d++;
                    while (e-- > c)
                        *(e + 1) = *e;
-                   *c = (char)0xff;
+                   *c = UTF_TO_NATIVE(0xff);
                    /* mark the range as done, and continue */
                    dorange = FALSE;
                    didrange = TRUE;
                    continue;
                }
+
                i = d - SvPVX(sv);              /* remember current offset */
                SvGROW(sv, SvLEN(sv) + 256);    /* never more than 256 chars in a range */
                d = SvPVX(sv) + i;              /* refresh d after realloc */
@@ -1297,8 +1307,8 @@ S_scan_const(pTHX_ char *start)
                if (didrange) {
                    Perl_croak(aTHX_ "Ambiguous range in transliteration operator");
                }
-               if (utf) {
-                   *d++ = (char)0xff;  /* use illegal utf8 byte--see pmtrans */
+               if (has_utf8) {
+                   *d++ = UTF_TO_NATIVE(0xff); /* use illegal utf8 byte--see pmtrans */
                    s++;
                    continue;
                }
@@ -1368,6 +1378,8 @@ S_scan_const(pTHX_ char *start)
                break;          /* in regexp, $ might be tail anchor */
        }
 
+       /* End of else if chain - OP_TRANS rejoin rest */
+
        /* backslashes */
        if (*s == '\\' && s+1 < send) {
            s++;
@@ -1430,14 +1442,14 @@ S_scan_const(pTHX_ char *start)
                ++s;
                if (*s == '{') {
                    char* e = strchr(s, '}');
+                   STRLEN len = 1;             /* allow underscores */
+
                    if (!e) {
                        yyerror("Missing right brace on \\x{}");
-                       e = s;
-                   }
-                   else {
-                       STRLEN len = 1;         /* allow underscores */
-                       uv = (UV)scan_hex(s + 1, e - s - 1, &len);
+                       ++s;
+                       continue;
                    }
+                   uv = (UV)scan_hex(s + 1, e - s - 1, &len);
                    s = e + 1;
                }
                else {
@@ -1502,7 +1514,6 @@ S_scan_const(pTHX_ char *start)
                            PL_sublex_info.sub_op->op_private |=
                                (PL_lex_repl ? OPpTRANS_FROM_UTF
                                             : OPpTRANS_TO_UTF);
-                           utf = TRUE;
                        }
                     }
                    else {
@@ -1603,40 +1614,40 @@ S_scan_const(pTHX_ char *start)
        } /* end if (backslash) */
 
     default_action:
-       if (!UTF8_IS_INVARIANT((U8)(*s)) && (this_utf8 || has_utf8)) {
-           STRLEN len = (STRLEN) -1;
-           UV uv;
-           if (this_utf8) {
-               uv = utf8n_to_uvchr((U8*)s, send - s, &len, 0);
-           }
-           if (len == (STRLEN)-1) {
-               /* Illegal UTF8 (a high-bit byte), make it valid. */
-               char *old_pvx = SvPVX(sv);
-               /* need space for one extra char (NOTE: SvCUR() not set here) */
-               d = SvGROW(sv, SvLEN(sv) + 1) + (d - old_pvx);
-               d = (char*)uvchr_to_utf8((U8*)d, (U8)*s++);
-           }
-           else {
-               while (len--)
-                   *d++ = *s++;
-           }
-           has_utf8 = TRUE;
-          if (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op) {
-              PL_sublex_info.sub_op->op_private |=
-                  (PL_lex_repl ? OPpTRANS_FROM_UTF : OPpTRANS_TO_UTF);
-              utf = TRUE;
-          }
-           continue;
-       }
-       *d++ = NATIVE_TO_NEED(has_utf8,*s++);
+       /* If we started with encoded form, or already know we want it
+          and then encode the next character */
+       if ((has_utf8 || this_utf8) && !NATIVE_IS_INVARIANT((U8)(*s))) {
+           STRLEN len  = 1;
+           UV uv       = (this_utf8) ? utf8n_to_uvchr((U8*)s, send - s, &len, 0) : (UV) ((U8) *s);
+           STRLEN need = UNISKIP(NATIVE_TO_UNI(uv));
+           s += len;
+           if (need > len) {
+               /* encoded value larger than old, need extra space (NOTE: SvCUR() not set here) */
+               STRLEN off = d - SvPVX(sv);
+               d = SvGROW(sv, SvLEN(sv) + (need-len)) + off;
+           }
+           d = (char*)uvchr_to_utf8((U8*)d, uv);
+           has_utf8 = TRUE;
+       }
+       else {
+           *d++ = NATIVE_TO_NEED(has_utf8,*s++);
+       }
     } /* while loop to process each character */
 
     /* terminate the string and set up the sv */
     *d = '\0';
     SvCUR_set(sv, d - SvPVX(sv));
+    if (SvCUR(sv) >= SvLEN(sv))
+      Perl_croak(aTHX_ "panic: constant overflowed allocated space");
+
     SvPOK_on(sv);
-    if (has_utf8)
+    if (has_utf8) {
        SvUTF8_on(sv);
+       if (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op) {
+               PL_sublex_info.sub_op->op_private |=
+                   (PL_lex_repl ? OPpTRANS_FROM_UTF : OPpTRANS_TO_UTF);
+       }
+    }
 
     /* shrink the sv if we allocated more than we used */
     if (SvCUR(sv) + 5 < SvLEN(sv)) {
@@ -2161,7 +2172,7 @@ Perl_yylex(pTHX)
        PL_pending_ident = 0;
 
        DEBUG_T({ PerlIO_printf(Perl_debug_log,
-              "### Tokener saw identifier '%s'\n", PL_tokenbuf); })
+              "### Tokener saw identifier '%s'\n", PL_tokenbuf); });
 
        /* if we're in a my(), we can't allow dynamics here.
           $foo'bar has already been turned into $foo::bar, so
@@ -2302,7 +2313,7 @@ Perl_yylex(pTHX)
        }
        DEBUG_T({ PerlIO_printf(Perl_debug_log,
               "### Next token after '%s' was known, type %"IVdf"\n", PL_bufptr,
-              (IV)PL_nexttype[PL_nexttoke]); })
+              (IV)PL_nexttype[PL_nexttoke]); });
 
        return(PL_nexttype[PL_nexttoke]);
 
@@ -2336,7 +2347,7 @@ Perl_yylex(pTHX)
        }
        else {
            DEBUG_T({ PerlIO_printf(Perl_debug_log,
-              "### Saw case modifier at '%s'\n", PL_bufptr); })
+              "### Saw case modifier at '%s'\n", PL_bufptr); });
            s = PL_bufptr + 1;
            if (strnEQ(s, "L\\u", 3) || strnEQ(s, "U\\l", 3))
                tmp = *s, *s = s[2], s[2] = tmp;        /* misordered... */
@@ -2388,7 +2399,7 @@ Perl_yylex(pTHX)
        if (PL_bufptr == PL_bufend)
            return sublex_done();
        DEBUG_T({ PerlIO_printf(Perl_debug_log,
-              "### Interpolated variable at '%s'\n", PL_bufptr); })
+              "### Interpolated variable at '%s'\n", PL_bufptr); });
        PL_expect = XTERM;
        PL_lex_dojoin = (*PL_bufptr == '@');
        PL_lex_state = LEX_INTERPNORMAL;
@@ -2488,7 +2499,7 @@ Perl_yylex(pTHX)
     DEBUG_T( {
        PerlIO_printf(Perl_debug_log, "### Tokener expecting %s at %s\n",
                      exp_name[PL_expect], s);
-    } )
+    } );
 
   retry:
     switch (*s) {
@@ -2507,7 +2518,7 @@ Perl_yylex(pTHX)
                yyerror("Missing right curly or square bracket");
             DEBUG_T( { PerlIO_printf(Perl_debug_log,
                         "### Tokener got EOF\n");
-            } )
+            } );
            TOKEN(0);
        }
        if (s++ < PL_bufend)
@@ -2840,6 +2851,8 @@ Perl_yylex(pTHX)
                s++;
            if (s < d)
                s++;
+           else if (s > d) /* Found by Ilya: feed random input to Perl. */
+             Perl_croak(aTHX_ "panic: input overflow");
            incline(s);
            if (PL_lex_formbrack && PL_lex_brackets <= PL_lex_formbrack) {
                PL_bufptr = s;
@@ -2867,7 +2880,7 @@ Perl_yylex(pTHX)
                s = force_word(PL_bufptr,WORD,FALSE,FALSE,FALSE);
                 DEBUG_T( { PerlIO_printf(Perl_debug_log,
                             "### Saw unary minus before =>, forcing word '%s'\n", s);
-                } )
+                } );
                OPERATOR('-');          /* unary minus */
            }
            PL_last_uni = PL_oldbufptr;
@@ -2912,7 +2925,7 @@ Perl_yylex(pTHX)
                PL_last_lop_op = ftst;
                DEBUG_T( { PerlIO_printf(Perl_debug_log,
                         "### Saw file test %c\n", (int)ftst);
-               } )
+               } );
                FTST(ftst);
            }
            else {
@@ -2921,7 +2934,7 @@ Perl_yylex(pTHX)
                DEBUG_T( { PerlIO_printf(Perl_debug_log,
                        "### %c looked like a file test but was not\n",
                        (int)ftst);
-               } )
+               } );
                s -= 2;
            }
        }
@@ -3218,8 +3231,16 @@ Perl_yylex(pTHX)
                else
                    PL_lex_brackstack[PL_lex_brackets++] = XOPERATOR;
                s = skipspace(s);
-               if (*s == '}')
+               if (*s == '}') {
+                   if (PL_expect == XREF && PL_lex_state == LEX_INTERPNORMAL) {
+                       PL_expect = XTERM;
+                       /* This hack is to get the ${} in the message. */
+                       PL_bufptr = s+1;
+                       yyerror("syntax error");
+                       break;
+                   }
                    OPERATOR(HASHBRACK);
+               }
                /* This hack serves to disambiguate a pair of curlies
                 * as being a block or an anon hash.  Normally, expectation
                 * determines that, but in cases where we're not in a
@@ -3681,7 +3702,7 @@ Perl_yylex(pTHX)
        s = scan_num(s, &yylval);
         DEBUG_T( { PerlIO_printf(Perl_debug_log,
                     "### Saw number in '%s'\n", s);
-        } )
+        } );
        if (PL_expect == XOPERATOR)
            no_op("Number",s);
        TERM(THING);
@@ -3690,7 +3711,7 @@ Perl_yylex(pTHX)
        s = scan_str(s,FALSE,FALSE);
         DEBUG_T( { PerlIO_printf(Perl_debug_log,
                     "### Saw string before '%s'\n", s);
-        } )
+        } );
        if (PL_expect == XOPERATOR) {
            if (PL_lex_formbrack && PL_lex_brackets == PL_lex_formbrack) {
                PL_expect = XTERM;
@@ -3709,7 +3730,7 @@ Perl_yylex(pTHX)
        s = scan_str(s,FALSE,FALSE);
         DEBUG_T( { PerlIO_printf(Perl_debug_log,
                     "### Saw string before '%s'\n", s);
-        } )
+        } );
        if (PL_expect == XOPERATOR) {
            if (PL_lex_formbrack && PL_lex_brackets == PL_lex_formbrack) {
                PL_expect = XTERM;
@@ -3734,7 +3755,7 @@ Perl_yylex(pTHX)
        s = scan_str(s,FALSE,FALSE);
         DEBUG_T( { PerlIO_printf(Perl_debug_log,
                     "### Saw backtick string before '%s'\n", s);
-        } )
+        } );
        if (PL_expect == XOPERATOR)
            no_op("Backticks",s);
        if (!s)
@@ -3764,7 +3785,7 @@ Perl_yylex(pTHX)
                TERM(THING);
            }
            /* avoid v123abc() or $h{v1}, allow C<print v10;> */
-           else if (!isALPHA(*start) && (PL_expect == XTERM || PL_expect == XREF)) {
+           else if (!isALPHA(*start) && (PL_expect == XTERM || PL_expect == XREF || PL_expect == XSTATE)) {
                char c = *start;
                GV *gv;
                *start = '\0';
@@ -3850,7 +3871,7 @@ Perl_yylex(pTHX)
            CLINE;
            yylval.opval = (OP*)newSVOP(OP_CONST, 0, newSVpv(PL_tokenbuf,0));
            yylval.opval->op_private = OPpCONST_BARE;
-           if (UTF && !IN_BYTE && is_utf8_string((U8*)PL_tokenbuf, len))
+           if (UTF && !IN_BYTES && is_utf8_string((U8*)PL_tokenbuf, len))
              SvUTF8_on(((SVOP*)yylval.opval)->op_sv);
            TERM(WORD);
        }
@@ -4011,7 +4032,7 @@ Perl_yylex(pTHX)
                if (*s == '=' && s[1] == '>') {
                    CLINE;
                    sv_setpv(((SVOP*)yylval.opval)->op_sv, PL_tokenbuf);
-                   if (UTF && !IN_BYTE && is_utf8_string((U8*)PL_tokenbuf, len))
+                   if (UTF && !IN_BYTES && is_utf8_string((U8*)PL_tokenbuf, len))
                      SvUTF8_on(((SVOP*)yylval.opval)->op_sv);
                    TERM(WORD);
                }
@@ -4175,13 +4196,19 @@ Perl_yylex(pTHX)
                        (void)PerlIO_seek(PL_rsfp, 0L, 0);
                    }
                    if (PerlLIO_setmode(PerlIO_fileno(PL_rsfp), O_TEXT) != -1) {
+#ifdef PERLIO_IS_STDIO /* really? */
+#  if defined(__BORLANDC__)
+                       /* XXX see note in do_binmode() */
+                       ((FILE*)PL_rsfp)->flags &= ~_F_BIN;
+#  endif
+#endif
                        if (loc > 0)
                            PerlIO_seek(PL_rsfp, loc, 0);
                    }
                }
 #endif
 #ifdef PERLIO_LAYERS
-               if (UTF && !IN_BYTE)
+               if (UTF && !IN_BYTES)
                    PerlIO_apply_layers(aTHX_ PL_rsfp, NULL, ":utf8");
 #endif
                PL_rsfp = Nullfp;
@@ -4970,7 +4997,7 @@ Perl_yylex(pTHX)
          really_sub:
            {
                char tmpbuf[sizeof PL_tokenbuf];
-               SSize_t tboffset;
+               SSize_t tboffset = 0;
                expectation attrful;
                bool have_name, have_proto;
                int key = tmp;
@@ -5614,7 +5641,7 @@ Perl_keyword(pTHX_ register char *d, I32 len)
            if (strEQ(d,"rindex"))              return -KEY_rindex;
            break;
        case 7:
-           if (strEQ(d,"require"))             return -KEY_require;
+           if (strEQ(d,"require"))             return KEY_require;
            if (strEQ(d,"reverse"))             return -KEY_reverse;
            if (strEQ(d,"readdir"))             return -KEY_readdir;
            break;
@@ -6509,7 +6536,7 @@ retval:
        Renew(SvPVX(tmpstr), SvLEN(tmpstr), char);
     }
     SvREFCNT_dec(herewas);
-    if (UTF && !IN_BYTE && is_utf8_string((U8*)SvPVX(tmpstr), SvCUR(tmpstr)))
+    if (UTF && !IN_BYTES && is_utf8_string((U8*)SvPVX(tmpstr), SvCUR(tmpstr)))
        SvUTF8_on(tmpstr);
     PL_lex_stuff = tmpstr;
     yylval.ival = op_type;
@@ -6863,11 +6890,11 @@ S_scan_str(pTHX_ char *start, int keep_quoted, int keep_delims)
 
   Read a number in any of the formats that Perl accepts:
 
-  0(x[0-7A-F]+)|([0-7]+)|(b[01])
-  [\d_]+(\.[\d_]*)?[Ee](\d+)
-
-  Underbars (_) are allowed in decimal numbers.  If -w is on,
-  underbars before a decimal point must be at three digit intervals.
+  \d(_?\d)*(\.(\d(_?\d)*)?)?[Ee][\+\-]?(\d(_?\d)*)     12 12.34 12.
+  \.\d(_?\d)*[Ee][\+\-]?(\d(_?\d)*)                    .34
+  0b[01](_?[01])*
+  0[0-7](_?[0-7])*
+  0x[0-9A-Fa-f](_?[0-9A-Fa-f])*
 
   Like most scan_ routines, it uses the PL_tokenbuf buffer to hold the
   thing it reads.
@@ -6937,8 +6964,17 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
            else if (s[1] == '.' || s[1] == 'e' || s[1] == 'E')
                goto decimal;
            /* so it must be octal */
-           else
+           else {
                shift = 3;
+               s++;
+           }
+
+           if (*s == '_') {
+              if (ckWARN(WARN_SYNTAX))
+                  Perl_warner(aTHX_ WARN_SYNTAX,
+                              "Misplaced _ in number");
+              lastub = s++;
+           }
 
            base = bases[shift];
            Base = Bases[shift];
@@ -6956,9 +6992,12 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
                default:
                    goto out;
 
-               /* _ are ignored */
+               /* _ are ignored -- but warned about if consecutive */
                case '_':
-                   s++;
+                   if (ckWARN(WARN_SYNTAX) && lastub && s == lastub + 1)
+                       Perl_warner(aTHX_ WARN_SYNTAX,
+                                   "Misplaced _ in number");
+                   lastub = s++;
                    break;
 
                /* 8 and 9 are not octal */
@@ -7025,6 +7064,13 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
             the number.
          */
          out:
+
+           /* final misplaced underbar check */
+           if (s[-1] == '_') {
+               if (ckWARN(WARN_SYNTAX))
+                   Perl_warner(aTHX_ WARN_SYNTAX, "Misplaced _ in number");
+           }
+
            sv = NEWSV(92,0);
            if (overflowed) {
                if (ckWARN(WARN_PORTABLE) && n > 4294967295.0)
@@ -7064,9 +7110,10 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
               if -w is on
            */
            if (*s == '_') {
-               if (ckWARN(WARN_SYNTAX) && lastub && s - lastub != 3)
-                   Perl_warner(aTHX_ WARN_SYNTAX, "Misplaced _ in number");
-               lastub = ++s;
+               if (ckWARN(WARN_SYNTAX) && lastub && s == lastub + 1)
+                   Perl_warner(aTHX_ WARN_SYNTAX,
+                               "Misplaced _ in number");
+               lastub = s++;
            }
            else {
                /* check for end of fixed-length buffer */
@@ -7078,7 +7125,7 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
        }
 
        /* final misplaced underbar check */
-       if (lastub && s - lastub != 3) {
+       if (lastub && s == lastub + 1) {
            if (ckWARN(WARN_SYNTAX))
                Perl_warner(aTHX_ WARN_SYNTAX, "Misplaced _ in number");
        }
@@ -7091,16 +7138,34 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
            floatit = TRUE;
            *d++ = *s++;
 
-           /* copy, ignoring underbars, until we run out of
-              digits.  Note: no misplaced underbar checks!
+           if (*s == '_') {
+               if (ckWARN(WARN_SYNTAX))
+                   Perl_warner(aTHX_ WARN_SYNTAX,
+                               "Misplaced _ in number");
+               lastub = s;
+           }
+
+           /* copy, ignoring underbars, until we run out of digits.
            */
            for (; isDIGIT(*s) || *s == '_'; s++) {
                /* fixed length buffer check */
                if (d >= e)
                    Perl_croak(aTHX_ number_too_long);
-               if (*s != '_')
+               if (*s == '_') {
+                  if (ckWARN(WARN_SYNTAX) && lastub && s == lastub + 1)
+                      Perl_warner(aTHX_ WARN_SYNTAX,
+                                  "Misplaced _ in number");
+                  lastub = s;
+               }
+               else
                    *d++ = *s;
            }
+           /* fractional part ending in underbar? */
+           if (s[-1] == '_') {
+               if (ckWARN(WARN_SYNTAX))
+                   Perl_warner(aTHX_ WARN_SYNTAX,
+                               "Misplaced _ in number");
+           }
            if (*s == '.' && isDIGIT(s[1])) {
                /* oops, it's really a v-string, but without the "v" */
                s = start - 1;
@@ -7109,22 +7174,48 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
        }
 
        /* read exponent part, if present */
-       if (*s && strchr("eE",*s) && strchr("+-0123456789",s[1])) {
+       if (*s && strchr("eE",*s) && strchr("+-0123456789_", s[1])) {
            floatit = TRUE;
            s++;
 
            /* regardless of whether user said 3E5 or 3e5, use lower 'e' */
            *d++ = 'e';         /* At least some Mach atof()s don't grok 'E' */
 
+           /* stray preinitial _ */
+           if (*s == '_') {
+               if (ckWARN(WARN_SYNTAX))
+                   Perl_warner(aTHX_ WARN_SYNTAX,
+                               "Misplaced _ in number");
+               lastub = s++;
+           }
+
            /* allow positive or negative exponent */
            if (*s == '+' || *s == '-')
                *d++ = *s++;
 
-           /* read digits of exponent (no underbars :-) */
-           while (isDIGIT(*s)) {
-               if (d >= e)
-                   Perl_croak(aTHX_ number_too_long);
-               *d++ = *s++;
+           /* stray initial _ */
+           if (*s == '_') {
+               if (ckWARN(WARN_SYNTAX))
+                   Perl_warner(aTHX_ WARN_SYNTAX,
+                               "Misplaced _ in number");
+               lastub = s++;
+           }
+
+           /* read digits of exponent */
+           while (isDIGIT(*s) || *s == '_') {
+               if (isDIGIT(*s)) {
+                   if (d >= e)
+                       Perl_croak(aTHX_ number_too_long);
+                   *d++ = *s++;
+               }
+               else {
+                  if (ckWARN(WARN_SYNTAX) &&
+                      ((lastub && s == lastub + 1) ||
+                       (!isDIGIT(s[1]) && s[1] != '_')))
+                      Perl_warner(aTHX_ WARN_SYNTAX,
+                                  "Misplaced _ in number");
+                  lastub = s++;
+               }
            }
        }
 
@@ -7143,8 +7234,8 @@ Perl_scan_num(pTHX_ char *start, YYSTYPE* lvalp)
         */
 
        if (!floatit) {
-           IV iv;
-           UV uv;
+           IV iv = 0;
+           UV uv = 0;
            errno = 0;
            if (*PL_tokenbuf == '-')
                iv = Strtol(PL_tokenbuf, (char**)NULL, 10);