Using indexes into the line instead of Vec<u8>s means we don't have to copy
the line to store the fields (indexes instead of slices because it avoids
self-referential structs). Using memchr also empirically saves a lot of
intermediate allocations.
- Change the main! proc_macro to a bin! macro_rules macro.
- Reexport uucore_procs from uucore
- Make utils to not import uucore_procs directly
- Remove the `syn` dependency and don't parse proc_macro input (hopefully for faster compile times)
Move the `printf::memo` module to `uucore` so that it can be used by
other programs, not just `printf`. For example, the `-f` option to `seq`
requires parsing and formatting numbers according to the same logic as
`printf`.
* seq: use BigDecimal to represent floats
Use `BigDecimal` to represent arbitrary precision floats in order to
prevent numerical precision issues when iterating over a sequence of
numbers. This commit makes several changes at once to accomplish this
goal.
First, it creates a new struct, `PreciseNumber`, that is responsible for
storing not only the number itself but also the number of digits (both
integer and decimal) needed to display it. This information is collected
at the time of parsing the number, which lives in the new
`numberparse.rs` module.
Second, it uses the `BigDecimal` struct to store arbitrary precision
floating point numbers instead of the previous `f64` primitive
type. This protects against issues of numerical precision when
repeatedly accumulating a very small increment.
Third, since neither the `BigDecimal` nor `BigInt` types have a
representation of infinity, minus infinity, minus zero, or NaN, we add
the `ExtendedBigDecimal` and `ExtendedBigInt` enumerations which extend
the basic types with these concepts.
* fixup! seq: use BigDecimal to represent floats
* fixup! seq: use BigDecimal to represent floats
* fixup! seq: use BigDecimal to represent floats
* fixup! seq: use BigDecimal to represent floats
* fixup! seq: use BigDecimal to represent floats
Replace the custom `split::walk_lines()` function with a call to
`std::io::copy()`, using a new `TakeLines` reader as the source and
`stdout` as the destination. The `TakeLines` reader is an adaptor that
scans the bytes being read for line ending characters and stops the
reading after a given number of lines has been read (similar to the
`std::io::Take` adaptor).
This change
* makes the `read_n_lines()` function more concise,
* allows it to mirror the implementation of `read_n_bytes()`,
* increases the speed of `head -n NUM`.
Since tac must read its input files completely to start processing them
from the end, it is particularly suited to use memory maps to benefit
from the page cache maintained by the operating systems to bring the
necessary data into memory as required.
This does also include situations where the input is stdin, but not via
a pipe but for example a file descriptor set up by the user's shell
through an input redirection.
