On Thu, Jul 09, 2009 at 12:54:07PM +0200, David Jander wrote: > On Thursday 09 July 2009 11:55:11 René Rebe wrote: > > Peter Hutterer wrote: > > > On Thu, Jul 09, 2009 at 11:01:54AM +0200, David Jander wrote: > > >> On Thursday 09 July 2009 02:04:59 Peter Hutterer wrote: > > >>> This patch adds the following three functions: > > >>> num_bytes_for_bits(bits) - the number of bytes needed to hold 'bits' > > >>> num_dwords_for_bytes(bytes) - the number of 4-byte units to hold > > >>> 'bytes' pad_to_dwords(bytes) - the closest multiple of 4 equal to or > > >>> larger than 'bytes'. > > >> > > >> Sorry to make this probably useless comment about naming, but while a > > >> byte has a defined length (8 bits), the meaning of "word" and "dword" in > > >> terms of length is undefined. By definition "word" in computing means > > >> the natural unit of data used by a particular computer design. This > > >> would be 32 bits on most 32-bit computers, and by consequence a "dword" > > >> would be 64 bit wide. Your definition of the names "word" and "dword" > > >> seem to be 16-bit platform-specific... not the most common platform for > > >> Xorg! > > >> Please, let's deprecate this flawed naming convention, and not use it in > > >> new code... it's confusing and just plain wrong when used on > > >> platform-independent code! > > > > > > This can be changed with a simple search+replace, I wouldn't mind > > > changing it. > > > > > > Please suggest a better alternative naming though, the only appropriate > > > equivalent I can think of is num_4byte_units_for_bytes and similar which > > > does make the function names a tad long. > > > > ...int8..., ...int16..., ...int32..., ... > > I agree. Although in theory 'int8' and 'byte' are of the same length (not > necessarily same type). > > If you want to make the names _really_ short, you might consider the > convention used in the linux kernel and some other places: u8, s8, u16, s16, > u32.... etc, very short and still readable ;-)
New patch below, new names are bits_to_bytes, bits_to_int32, pad_to_int32. I think these are short enough, not as clumsy as the num_a_from_b and int32 is more precise than dword. I don't think we need to worry about the size of a byte anymore... I won't send all new patches since they are just search+replace, if needed they are available on git://people.freedesktop.org/~whot/xserver.git bytecounting Thanks for all the comments, I really didn't think of int32 and the like. Cheers, Peter >From 0042708b708b868a4eac91426beee3dd68820421 Mon Sep 17 00:00:00 2001 From: Peter Hutterer <[email protected]> Date: Mon, 29 Jun 2009 13:09:57 +1000 Subject: [PATCH] include: introduce byte counting functions. This patch adds the following three functions: bits_to_bytes(bits) - the number of bytes needed to hold 'bits' bytes_to_int32(bytes) - the number of 4-byte units to hold 'bytes' pad_to_int32(bytes) - the closest multiple of 4 equal to or larger than 'bytes'. All three operations are common in protocol processing and currently the server has ((foo + 7)/8 + 3)/4 operations all over the place. A common set of functions reduce the error rate of these (albeit simple) calculations and improve readability of the code. The functions do not check for overflow. Signed-off-by: Peter Hutterer <[email protected]> --- include/misc.h | 30 ++++++++++++++++++++++++++++++ test/input.c | 39 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 69 insertions(+), 0 deletions(-) diff --git a/include/misc.h b/include/misc.h index 61dd947..877c682 100644 --- a/include/misc.h +++ b/include/misc.h @@ -180,6 +180,36 @@ typedef struct _xReq *xReqPtr; #endif +/** + * Calculate the number of bytes needed to hold bits. + * @param bits The minimum number of bits needed. + * @return The number of bytes needed to hold bits. + */ +static inline int +bits_to_bytes(const int bits) { + return ((bits + 7) >> 3); +} +/** + * Calculate the number of 4-byte units needed to hold the given number of + * bytes. + * @param bytes The minimum number of bytes needed. + * @return The number of 4-byte units needed to hold bytes. + */ +static inline int +bytes_to_int32(const int bytes) { + return (((bytes) + 3) >> 2); +} + +/** + * Calculate the number of bytes (in multiples of 4) needed to hold bytes. + * @param bytes The minimum number of bytes needed. + * @return The closest multiple of 4 that is equal or higher than bytes. + */ +static inline int +pad_to_int32(const int bytes) { + return (((bytes) + 3) & ~3); +} + /* some macros to help swap requests, replies, and events */ #define LengthRestB(stuff) \ diff --git a/test/input.c b/test/input.c index bb32491..e2faaef 100644 --- a/test/input.c +++ b/test/input.c @@ -678,6 +678,44 @@ static void dix_grab_matching(void) g_assert(rc == TRUE); } +static void include_byte_padding_macros(void) +{ + int i; + g_test_message("Testing bits_to_bytes()"); + + /* the macros don't provide overflow protection */ + for (i = 0; i < INT_MAX - 7; i++) + { + int expected_bytes; + expected_bytes = (i + 7)/8; + + g_assert(bits_to_bytes(i) >= i/8); + g_assert((bits_to_bytes(i) * 8) - i <= 7); + } + + g_test_message("Testing bytes_to_int32()"); + for (i = 0; i < INT_MAX - 3; i++) + { + int expected_4byte; + expected_4byte = (i + 3)/4; + + g_assert(bytes_to_int32(i) <= i); + g_assert((bytes_to_int32(i) * 4) - i <= 3); + } + + g_test_message("Testing pad_to_int32"); + + for (i = 0; i < INT_MAX - 3; i++) + { + int expected_bytes; + expected_bytes = ((i + 3)/4) * 4; + + g_assert(pad_to_int32(i) >= i); + g_assert(pad_to_int32(i) - i <= 3); + } + +} + int main(int argc, char** argv) { g_test_init(&argc, &argv,NULL); @@ -688,6 +726,7 @@ int main(int argc, char** argv) g_test_add_func("/dix/input/check-grab-values", dix_check_grab_values); g_test_add_func("/dix/input/xi2-struct-sizes", xi2_struct_sizes); g_test_add_func("/dix/input/grab_matching", dix_grab_matching); + g_test_add_func("/include/byte_padding_macros", include_byte_padding_macros); return g_test_run(); } -- 1.6.3.rc1.2.g0164.dirty _______________________________________________ xorg-devel mailing list [email protected] http://lists.x.org/mailman/listinfo/xorg-devel
