I just re-checked with ltrace, and yes you're right, it does in fact call snprintf() and frexp() to format floats.

I had done a similar check some time ago, and was surprised to not find any libc calls related to Perl's s/printf()  (which is why I posted) — but that must have been without a float format specifier being used... (rather only integer formatting like %d, %u etc.)   As to the creation of floats, however, I don't see any calls to libc or libm. Any idea what function that would be (just out of curiosity)?

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).