wide-int-print: Don't print large numbers hexadecimally for print_dec{,s,u}

wide-int-print: Don't print large numbers hexadecimally for print_dec{,s,u}

The following patch implements printing of wide_int/widest_int numbers
decimally when asked for that using print_dec{,s,u}, even if they have
precision larger than 64 and get_len () above 1 (right now we printed
them hexadecimally and even negative numbers as huge positive hexadecimal).

In order to avoid the expensive division/modulo by 10^19 twice, once to
estimate how many will be needed and another to actually print it, the
patch prints the 19 digit chunks in reverse order (from least significant
to most significant) and then reorders those with linear complexity to form
the right printed number.
Tested with printing both 256 and 320 bit numbers (first as an example
of even number of 19 digit chunks plus one shorter above it, the second
as an example of odd number of 19 digit chunks plus one shorter above it).

The l * HOST_BITS_PER_WIDE_INT / 3 + 3 estimatition thinking about it now
is one byte too much (one byte for -, one for '\0') and too conservative,
so we could go with l * HOST_BITS_PER_WIDE_INT / 3 + 2 as well, or e.g.
l * HOST_BITS_PER_WIDE_INT * 10 / 33 + 3 as even less conservative
estimation (though more expensive to compute in inline code).
But that l * HOST_BITS_PER_WIDE_INT / 4 + 4; is likely one byte too much
as well, 2 bytes for 0x, one byte for '\0' and where does the 4th one come
from?  Of course all of these assuming HOST_BITS_PER_WIDE_INT is a multiple
of 64...

2023-10-17  Jakub Jelinek  <jakub@redhat.com>

	* wide-int-print.h (print_dec_buf_size): For length, divide number
	of bits by 3 and add 3 instead of division by 4 and adding 4.
	* wide-int-print.cc (print_decs): Remove superfluous ()s.  Don't call
	print_hex, instead call print_decu on either negated value after
	printing - or on wi itself.
	(print_decu): Don't call print_hex, instead print even large numbers
	decimally.
	(pp_wide_int_large): Assume len from print_dec_buf_size is big enough
	even if it returns false.
	* pretty-print.h (pp_wide_int): Use print_dec_buf_size to check if
	pp_wide_int_large should be used.
	* tree-pretty-print.cc (dump_generic_node): Use print_hex_buf_size
	to compute needed buffer size.