Text representation of a float formatted using given options.

This BIF solves a problem of float_to_list/1 that doesn't allow
specifying the number of digits after the decimal point when
formatting floats.

    float_to_list(Float, Options) -> string()

    Float = float()
    Options = [Option]
    Option = {decimals, Decimals::0..249} |
             {scientific, Decimals::0..249} |
             compact

Returns a string which corresponds to the text representation of
a `Float` formatted using given options.

When decimals option is specified the returned value will contain
at most `Decimals` number of digits past the decimal point.
When `compact` option is provided the trailing zeros at the end
of the list are truncated (this option is only meaningful together
with the `decimals` option). When `scientific` option is provided,
the float will be formatted using scientific notation with
`Decimals` digits of precision. If `Options` is `[]` the function
behaves like `float_to_list/1`. When using `decimals` option and
the number doesn't fit in the static internal buffer of 256 bytes
the function throws `badarg`.

1 files changed, 3 insertions, 0 deletions

diff --git a/erts/emulator/beam/sys.h b/erts/emulator/beam/sys.h
index 898a30b010..cecaff54a4 100644
--- a/erts/emulator/beam/sys.h
+++ b/erts/emulator/beam/sys.h
@@ -729,9 +729,12 @@ char * getenv_string(GETENV_STATE *);
 void fini_getenv_state(GETENV_STATE *);
 
 /* xxxP */
+#define SYS_DEFAULT_FLOAT_DECIMALS 20
 void init_sys_float(void);
 int sys_chars_to_double(char*, double*);
 int sys_double_to_chars(double, char*, size_t);
+int sys_double_to_chars_ext(double, char*, size_t, size_t);
+int sys_double_to_chars_fast(double, char*, int, int, int);
 void sys_get_pid(char *, size_t);
 
 /* erts_sys_putenv() returns, 0 on success and a value != 0 on failure. */