toke.c

13286         if (floatit) {
13287             /* terminate the string */
13288             *d = '\0';
13289             nv = Atof(PL_tokenbuf);
13290             sv_setnv(sv, nv);
13291         }
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I didn't track Atof all the way through since I found comments in perl.h indicate Perl usually uses Perl's own atof implementation, but it can be configured to the native implementation (and does so on UNICOS).