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SubjectRe: [RFCv3][PATCH 1/4] replace string_get_size() arrays
On Fri, 30 Sep 2011, Dave Hansen wrote:

>
> Instead of explicitly storing the entire string for each
> possible units, just store the thing that varies: the
> first character.
>
> We have to special-case the 'B' unit (index==0).
>
> This shaves about 100 bytes off of my .o file.
>

It shaved more than that from my .o file, but should we really be
optimizing this for text size? __unit_str() would be replacing what used
to be a read of stack-allocated memory and make string_get_size() more
expensive of a function and more complex code.

> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
> ---
>
> linux-2.6.git-dave/lib/string_helpers.c | 30 ++++++++++++++++++++----------
> 1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff -puN lib/string_helpers.c~string_get_size-pow2 lib/string_helpers.c
> --- linux-2.6.git/lib/string_helpers.c~string_get_size-pow2 2011-09-30 16:50:31.628981352 -0700
> +++ linux-2.6.git-dave/lib/string_helpers.c 2011-09-30 17:04:02.211607364 -0700
> @@ -8,6 +8,23 @@
> #include <linux/module.h>
> #include <linux/string_helpers.h>
>
> +static const char byte_units[] = "_KMGTPEZY";
> +
> +static char *__units_str(enum string_size_units unit, char *buf, int index)
> +{
> + int place = 0;
> +
> + /* index=0 is plain 'B' with no other unit */
> + if (index) {
> + buf[place++] = byte_units[index];
> + if (unit == STRING_UNITS_2)
> + buf[place++] = 'i';
> + }
> + buf[place++] = 'B';
> + buf[place++] = '\0';
> + return buf;
> +}
> +
> /**
> * string_get_size - get the size in the specified units
> * @size: The size to be converted
> @@ -23,26 +40,19 @@
> int string_get_size(u64 size, const enum string_size_units units,
> char *buf, int len)
> {
> - const char *units_10[] = { "B", "kB", "MB", "GB", "TB", "PB",
> - "EB", "ZB", "YB", NULL};
> - const char *units_2[] = {"B", "KiB", "MiB", "GiB", "TiB", "PiB",
> - "EiB", "ZiB", "YiB", NULL };
> - const char **units_str[] = {
> - [STRING_UNITS_10] = units_10,
> - [STRING_UNITS_2] = units_2,
> - };
> const unsigned int divisor[] = {
> [STRING_UNITS_10] = 1000,
> [STRING_UNITS_2] = 1024,
> };
> int i, j;
> u64 remainder = 0, sf_cap;
> + char unit_buf[4];
> char tmp[8];
>
> tmp[0] = '\0';
> i = 0;
> if (size >= divisor[units]) {
> - while (size >= divisor[units] && units_str[units][i]) {
> + while (size >= divisor[units] && (i < strlen(byte_units))) {
> remainder = do_div(size, divisor[units]);
> i++;
> }
> @@ -61,7 +71,7 @@ int string_get_size(u64 size, const enum
> }
>
> snprintf(buf, len, "%lld%s %s", (unsigned long long)size,
> - tmp, units_str[units][i]);
> + tmp, __units_str(units, unit_buf, i));
>
> return 0;
> }


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