avoid negative shift in scan_num()

Lengthy binaryish floating point literals used to perform illegal bit
shifts.  Ignore digits that are past the end of the significand at an
earlier stage to avoid this.  Code fix by Tony C.  Fixes [perl #131894].

1 files changed, 1 insertions, 1 deletions

diff --git a/toke.c b/toke.c
index 0b3e2aaf76..3baa520131 100644
--- a/toke.c
+++ b/toke.c
@@ -11091,7 +11091,7 @@ Perl_scan_num(pTHX_ const char *start, YYSTYPE* lvalp)
                                     hexfp_uquad <<= shift;
                                     hexfp_uquad |= b;
                                     hexfp_frac_bits += shift;
-                                } else {
+                                } else if (significant_bits - shift < NV_MANT_DIG) {
                                     /* We are at a hexdigit either at,
                                      * or straddling, the edge of mantissa.
                                      * We will try grabbing as many as