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 C README
 ========
 This "shar" file contains the documentation for the
 electronic mail distribution of the Dhrystone benchmark (C version 2.1);
 a companion "shar" file contains the source code.
 (Because of mail length restrictions for some mailers, I have
 split the distribution in two parts.)
 
 For versions in other languages, see the other "shar" files.
 
 Files containing the C version (*.h: Header File, *.c: C Modules)
 
   dhry.h
   dhry_1.c
   dhry_2.c
   
 The file RATIONALE contains the article 
 
   "Dhrystone Benchmark: Rationale for Version 2 and Measurement Rules"
 
 which has been published, together with the C source code (Version 2.0),
 in SIGPLAN Notices vol. 23, no. 8 (Aug. 1988), pp. 49-62.
 This article explains all changes that have been made for Version 2,
 compared with the version of the original publication
 in Communications of the ACM vol. 27, no. 10 (Oct. 1984), pp. 1013-1030.
 It also contains "ground rules" for benchmarking with Dhrystone
 which should be followed by everyone who uses the program and publishes
 Dhrystone results.
 
 Compared with the Version 2.0 published in SIGPLAN Notices, Version 2.1
 contains a few corrections that have been made after Version 2.0 was
 distriobuted over the UNIX network Usenet. These small differences between
 Version 2.0 and 2.1 should not affect execution time measurements.
 For those who want to compare the exact contents of both versions,
 the file "dhry_c.dif" contains the differences between the two versions,
 as generated by a file comparison of the corresponding files with the
 UNIX utility "diff".
 
 The file VARIATIONS contains the article
 
   "Understanding Variations in Dhrystone Performance"
 
 which has been published in Microprocessor Report, May 1989
 (Editor: M. Slater), pp. 16-17. It describes the points that users
 should know if C Dhrystone results are compared.
 
 Recipients of this shar file who perform measurements are asked
 to send measurement results to the author and/or to Rick Richardson.
 Rick Richardson publishes regularly Dhrystone results on the UNIX network
 Usenet. For submissions of results to him (preferably by electronic mail,
 see address in the program header), he has provided a form which is contained
 in the file "submit.frm".
 
 
 The following files are contained in other "shar" files:
 
 Files containing the Ada version (*.s: Specifications, *.b: Bodies):
 
   d_global.s
   d_main.b
   d_pack_1.b
   d_pack_1.s
   d_pack_2.b
   d_pack_2.s
 
 File containing the Pascal version:
 
   dhry.p
 
 
 February 22, 1990
 
                  Reinhold P. Weicker
                  Siemens AG, AUT E 51
                  Postfach 3220
                  D-8520 Erlangen
                  Germany (West)
 
                  Phone:  [xxx-49]-9131-7-20330  (8-17 Central European Time)
                  UUCP:   ..!mcsun!unido!estevax!weicker
 
 
 Rationale
 =========
 
 
 
     Dhrystone Benchmark: Rationale for Version 2 and Measurement Rules
 
         [published in SIGPLAN Notices 23,8 (Aug. 1988), 49-62]
 
 
                  Reinhold P. Weicker
                  Siemens AG, E STE 35
                  [now: Siemens AG, AUT E 51]
                  Postfach 3220
                  D-8520 Erlangen
                  Germany (West)
 
 
 
 
 1.  Why a Version 2 of Dhrystone?
 
 The Dhrystone benchmark  program  [1]  has  become  a  popular  benchmark  for
 CPU/compiler   performance   measurement,   in   particular  in  the  area  of
 minicomputers, workstations, PC's and microprocesors.  It apparently satisfies
 a  need  for  an  easy-to-use  integer benchmark; it gives a first performance
 indication which is more meaningful than MIPS numbers which, in their  literal
 meaning  (million  instructions  per  second), cannot be used across different
 instruction sets (e.g. RISC  vs.  CISC).   With  the  increasing  use  of  the
 benchmark, it seems necessary to reconsider the benchmark and to check whether
 it can still fulfill this function.  Version 2 of Dhrystone is the  result  of
 such a re-evaluation, it has been made for two reasons:
 
 o Dhrystone has been published in Ada [1], and Versions in Ada, Pascal  and  C
   have  been  distributed  by  Reinhold Weicker via floppy disk.  However, the
   version that was used most often for benchmarking has been the version  made
   by  Rick  Richardson  by another translation from the Ada version into the C
   programming language, this has been the version  distributed  via  the  UNIX
   network Usenet [2].
 
   There is an obvious need for a common C version of Dhrystone, since C is  at
   present  the  most  popular  system  programming  language  for the class of
   systems (microcomputers, minicomputers,  workstations)  where  Dhrystone  is
   used  most.   There  should  be,  as  far as possible, only one C version of
   Dhrystone such that results can be compared  without  restrictions.  In  the
   past,  the  C  versions  distributed by Rick Richardson (Version 1.1) and by
   Reinhold Weicker had small (though not significant) differences.
 
   Together with the new C version, the  Ada  and  Pascal  versions  have  been
   updated as well.
 
 o As far as it is  possible  without  changes  to  the  Dhrystone  statistics,
   optimizing   compilers   should   be  prevented  from  removing  significant
   statements.  It has  turned  out  in  the  past  that  optimizing  compilers
   suppressed  code  generation for too many statements (by "dead code removal"
   or  "dead  variable  elimination").   This  has  lead  to  the  danger  that
   benchmarking  results obtained by a naive application of Dhrystone - without
   inspection of the code that was generated - could become meaningless.
 
 The  overall  policiy  for  version  2  has  been  that  the  distribution  of
 statements,  operand types and operand locality described in [1] should remain
 unchanged as much as possible.  (Very few changes were necessary; their impact
 should be negligible.)  Also, the order of statements should remain unchanged.
 Although I am aware of some critical remarks on the benchmark - I  agree  with
 several  of them - and know some suggestions for improvement, I didn't want to
 change the benchmark into something different from what has  become  known  as
 "Dhrystone"; the confusion generated by such a change would probably outweight
 the benefits. If I were to write a new benchmark program, I wouldn't  give  it
 the  name  "Dhrystone"  since  this  denotes  the  program  published  in [1].
 However, I do recognize  the  need  for  a  larger  number  of  representative
 programs  that can be used as benchmarks; users should always be encouraged to
 use more than just one benchmark.
 
 The new versions (version 2.1 for C, Pascal and Ada) will  be  distributed  as
 widely as possible.  (Version 2.1 differs from version 2.0 distributed via the
 UNIX Network Usenet in  March  1988  only  in  a  few  corrections  for  minor
 deficiencies  found  by  users  of  version 2.0.)  Readers who want to use the
 benchmark for their own measurements can obtain  a  copy  in  machine-readable
 form on floppy disk (MS-DOS or XENIX format) from the author.
 
 
 2.  Overall Characteristics of Version 2
 
 In general, version 2  follows  -  in  the  parts  that  are  significant  for
 performance  measurement,  i.e.   within  the measurement loop - the published
 (Ada) version and the C versions previously distributed.  Where  the  versions
 distributed  by  Rick Richardson [2] and Reinhold Weicker have been different,
 it  follows  the  version  distributed  by  Reinhold  Weicker.  (However,  the
 differences  have  been  so  small  that their impact on execution time in all
 likelihood has been negligible.)  The initialization and UNIX  instrumentation
 part  -  which  had  been  omitted  in  [1] - follows mostly the ideas of Rick
 Richardson [2].  However, any changes in the initialization part  and  in  the
 printing  of  the  result have no impact on performance measurement since they
 are outside the measaurement loop.  As a concession to older compilers,  names
 have been made unique within the first 8 characters for the C version.
 
 The original publication of Dhrystone did not contain any statements for  time
 measurement  since  they  are necessarily system-dependent. However, it turned
 out that it is not enough just to inclose the main procedure of Dhrystone in a
 loop  and  to  measure the execution time.  If the variables that are computed
 are not used somehow, there is the danger that the compiler considers them  as
 "dead  variables" and suppresses code generation for a part of the statements.
 Therefore in version 2 all variables of "main" are printed at the end  of  the
 program.  This also permits some plausibility control for correct execution of
 the benchmark.
 
 At several places in the benchmark, code has been added, but only in  branches
 that  are  not  executed. The intention is that optimizing compilers should be
 prevented from moving code out of the measurement loop, or from removing  code
 altogether.  Statements that are executed have been changed in very few places
 only.  In these cases, only the role of some operands has been changed, and it
 was   made  sure  that  the  numbers  defining  the  "Dhrystone  distribution"
 (distribution of statements, operand types and locality) still hold as much as
 possible.   Except for sophisticated optimizing compilers, execution times for
 version 2.1 should be the same as for previous versions.
 
 Because of the self-imposed limitation that the order and distribution of  the
 executed  statements  should  not  be  changed,  there  are  still cases where
 optimizing compilers may not generate code for some statements. To  a  certain
 degree,  this  is  unavoidable  for  small synthetic benchmarks.  Users of the
 benchmark are advised to check code listings whether code is generated for all
 statements of Dhrystone.
 
 Contrary to the suggestion in the published paper and its realization  in  the
 versions previously distributed, no attempt has been made to subtract the time
 for the measurement loop overhead. (This calculation has proven  difficult  to
 implement  in  a  correct  way,  and  its omission makes the program simpler.)
 However, since the loop check is now part of the benchmark, this does have  an
 impact  -  though a very minor one - on the distribution statistics which have
 been updated for this version.
 
 
 3.  Discussion of Individual Changes
 
 In this section, all changes are described that affect  the  measurement  loop
 and  that  are  not  just  renamings  of variables. All remarks refer to the C
 version; the other language versions have been updated similarly.
 
 In addition to adding  the  measurement  loop  and  the  printout  statements,
 changes have been made at the following places:
 
 o In procedure "main", three statements have been added  in  the  non-executed
   "then" part of the statement
 
         if (Enum_Loc == Func_1 (Ch_Index, 'C'))
 
   they are
 
         strcpy (Str_2_Loc, "DHRYSTONE PROGRAM, 3'RD STRING");
         Int_2_Loc = Run_Index;
         Int_Glob = Run_Index;
 
   The string assignment prevents  movement  of  the  preceding  assignment  to
   Str_2_Loc  (5'th  statement  of  "main")  out  of the measurement loop (This
   probably will not happen for the C version, but it did happen  with  another
   language   and  compiler.)   The  assignment  to  Int_2_Loc  prevents  value
   propagation for Int_2_Loc, and the assignment to Int_Glob makes the value of
   Int_Glob possibly dependent from the value of Run_Index.
 
 o In the three arithmetic computations at the end of the measurement  loop  in
   "main  ",  the  role  of  some  variables has been exchanged, to prevent the
   division from just cancelling out the multiplication as it was  in  [1].   A
   very   smart  compiler  might  have  recognized  this  and  suppressed  code
   generation for the division.
 
 o For Proc_2, no code has been changed, but the values of the actual parameter
   have changed due to changes in "main".
 
 o In Proc_4, the second assignment has been changed from
 
         Bool_Loc = Bool_Loc | Bool_Glob;
 
   to
 
         Bool_Glob = Bool_Loc | Bool_Glob;
 
   It now assigns a value to a global variable  instead  of  a  local  variable
   (Bool_Loc);   Bool_Loc  would  be  a  "dead  variable"  which  is  not  used
   afterwards.
 
 o In Func_1, the statement
 
         Ch_1_Glob = Ch_1_Loc;
 
   was added in the non-executed "else" part of the "if" statement, to  prevent
   the suppression of code generation for the assignment to Ch_1_Loc.
 
 o In Func_2, the second character comparison statement has been changed to
 
         if (Ch_Loc == 'R')
 
   ('R' instead of 'X') because  a  comparison  with  'X'  is  implied  in  the
   preceding "if" statement.
 
   Also in Func_2, the statement
 
         Int_Glob = Int_Loc;
 
   has been added in the non-executed part of the last "if" statement, in order
   to prevent Int_Loc from becoming a dead variable.
 
 o In Func_3, a non-executed "else" part has been added to the "if"  statement.
   While  the  program  would  not be incorrect without this "else" part, it is
   considered bad programming practice if a function  can  be  left  without  a
   return value.
 
   To compensate for this change, the (non-executed) "else" part  in  the  "if"
   statement of Proc_3 was removed.
 
 The distribution statistics have been changed only  by  the  addition  of  the
 measurement loop iteration (1 additional statement, 4 additional local integer
 operands) and by the change in Proc_4  (one  operand  changed  from  local  to
 global).  The distribution statistics in the comment headers have been updated
 accordingly.
 
 
 4.  String Operations
 
 The string operations (string assignment and string comparison) have not  been
 changed, to keep the program consistent with the original version.
 
 There has been some concern that the string operations are over-represented in
 the  program,  and that execution time is dominated by these operations.  This
 was true in particular when optimizing compilers removed too much code in  the
 main part of the program, this should have been mitigated in version 2.
 
 It should be noted that this is a  language-dependent  issue:   Dhrystone  was
 first  published  in  Ada, and with Ada or Pascal semantics, the time spent in
 the string operations is,  at  least  in  all  implementations  known  to  me,
 considerably smaller.  In Ada and Pascal, assignment and comparison of strings
 are operators defined in the language, and the upper  bounds  of  the  strings
 occuring  in  Dhrystone  are part of the type information known at compilation
 time.  The compilers can therefore generate  efficient  inline  code.   In  C,
 string  assignemt  and comparisons are not part of the language, so the string
 operations must be expressed in terms of the C library functions "strcpy"  and
 "strcmp".   (ANSI  C  allows  an  implementation  to use inline code for these
 functions.)  In addition to the overhead caused by additional function  calls,
 these  functions  are  defined for null-terminated strings where the length of
 the strings is not known at compilation time; the function has to check  every
 byte for the termination condition (the null byte).
 
 Obviously, a C library which includes efficiently coded "strcpy" and  "strcmp"
 functions  helps to obtain good Dhrystone results. However, I don't think that
 this is unfair since string  functions  do  occur  quite  frequently  in  real
 programs  (editors, command interpreters, etc.).  If the strings functions are
 implemented efficiently,  this  helps  real  programs  as  well  as  benchmark
 programs.
 
 I admit that the  string  comparison  in  Dhrystone  terminates  later  (after
 scanning  20  characters)  than most string comparisons in real programs.  For
 consistency with the original benchmark, I didn't change the  program  despite
 this weakness.
 
 
 5.  Intended Use of Dhrystone
 
 When Dhrystone is used, the following "ground rules" apply:
 
 o Separate compilation (Ada and C versions)
 
   As mentioned in [1], Dhrystone was written  to  reflect  actual  programming
   practice  in  systems  programming.   The  division into several compilation
   units (5 in the Ada version, 2 in the C version)  is  intended,  as  is  the
   distribution of inter-module and intra-module subprogram calls.  Although on
   many systems there will be no difference in execution time  to  a  Dhrystone
   version  where  all  compilation units are merged into one file, the rule is
   that separate compilation should  be  used.   The  intention  is  that  real
   programming  practice,  where  programs  consist  of  several  independently
   compiled units, should  be  reflected.   This  also  has  implies  that  the
   compiler,  while  compiling  one  unit,  has no information about the use of
   variables, register allocation etc.  occuring in  other  compilation  units.
   Although  in  real  life  compilation  units  will  probably  be larger, the
   intention is that these effects  of  separate  compilation  are  modeled  in
   Dhrystone.
 
   A few language systems have post-linkage optimization available (e.g., final
   register allocation is performed after linkage).  This is a borderline case:
   Post-linkage  optimization  involves  additional  program  preparation  time
   (although  not  as  much  as  compilation in one unit) which may prevent its
   general use in practical programming.  I think that  since  it  defeats  the
   intentions given above, it should not be used for Dhrystone.
 
   Unfortunately, ISO/ANSI  Pascal  does  not  contain  language  features  for
   separate  compilation.   Although  most  commercial Pascal compilers provide
   separate compilation in some way, we cannot use it for Dhrystone since  such
   a  version  would  not  be portable.  Therefore, no attempt has been made to
   provide a Pascal version with several compilation units.
 
 o No procedure merging
 
   Although Dhrystone contains some very short procedures where execution would
   benefit  from  procedure  merging (inlining, macro expansion of procedures),
   procedure merging is not to be used.  The reason is that the  percentage  of
   procedure  and  function  calls  is  part of the "Dhrystone distribution" of
   statements contained in [1].  This restriction does not hold for the  string
   functions  of  the  C  version  since ANSI C allows an implementation to use
   inline code for these functions.
 
 o Other optimizations are allowed, but they should be indicated
 
   It is often hard to draw an exact line between "normal code generation"  and
   "optimization"  in  compilers:  Some compilers perform operations by default
   that are invoked in other compilers only  when  optimization  is  explicitly
   requested.  Also, we cannot avoid that in benchmarking people try to achieve
   results that look as good as possible.  Therefore,  optimizations  performed
   by  compilers  -  other  than  those  listed  above - are not forbidden when
   Dhrystone execution times are measured.  Dhrystone is  not  intended  to  be
   non-optimizable  but  is  intended  to  be  similarly  optimizable as normal
   programs.   For  example,  there  are  several  places  in  Dhrystone  where
   performance   benefits   from   optimizations   like   common  subexpression
   elimination, value  propagation  etc.,  but  normal  programs  usually  also
   benefit  from  these  optimizations.   Therefore,  no  effort  was  made  to
   artificially  prevent  such  optimizations.   However,  measurement  reports
   should  indicate  which  compiler  optimization  levels  have been used, and
   reporting results with different levels of  compiler  optimization  for  the
   same hardware is encouraged.
 
 o Default results are those without "register" declarations (C version)
 
   When Dhrystone results are quoted  without  additional  qualification,  they
   should  be  understood  as  results  obtained  without use of the "register"
   attribute. Good compilers should be able to make good use of registers  even
   without explicit register declarations ([3], p. 193).
 
 Of course, for experimental  purposes,  post-linkage  optimization,  procedure
 merging and/or compilation in one unit can be done to determine their effects.
 However,  Dhrystone  numbers  obtained  under  these  conditions   should   be
 explicitly  marked as such; "normal" Dhrystone results should be understood as
 results obtained following the ground rules listed above.
 
 In any case, for serious performance evaluation, users are advised to ask  for
 code  listings  and  to  check  them carefully.  In this way, when results for
 different systems are  compared,  the  reader  can  get  a  feeling  how  much
 performance  difference is due to compiler optimization and how much is due to
 hardware speed.
 
 
 6.  Acknowledgements
 
 The C version 2.1 of Dhrystone has been developed  in  cooperation  with  Rick
 Richardson  (Tinton  Falls,  NJ), it incorporates many ideas from the "Version
 1.1" distributed previously by him over the UNIX network Usenet.  Through  his
 activity with Usenet, Rick Richardson has made a very valuable contribution to
 the dissemination of the benchmark.  I also thank  Chaim  Benedelac  (National
 Semiconductor),  David Ditzel (SUN), Earl Killian and John Mashey (MIPS), Alan
 Smith and Rafael  Saavedra-Barrera  (UC  at  Berkeley)  for  their  help  with
 comments on earlier versions of the benchmark.
 
 
 7.  Bibliography
 
 [1]
    Reinhold P. Weicker: Dhrystone: A Synthetic Systems Programming Benchmark.
    Communications of the ACM 27, 10 (Oct. 1984), 1013-1030
 
 [2]
    Rick Richardson: Dhrystone 1.1 Benchmark Summary (and Program Text)
    Informal Distribution via "Usenet", Last Version Known  to  me:  Sept.  21,
    1987
 
 [3]
    Brian W. Kernighan and Dennis M. Ritchie:  The C Programming Language.
    Prentice-Hall, Englewood Cliffs (NJ) 1978
 
 
 Variations
 ==========
             Understanding Variations in Dhrystone Performance
 
 
 
           By Reinhold P. Weicker, Siemens AG, AUT E 51, Erlangen
 
 
 
                                 April 1989
 
 
                       This article has appeared in:
 
 
         Microprocessor Report, May 1989 (Editor: M. Slater), pp. 16-17
 
 
 
 
 Microprocessor manufacturers tend to credit all the  performance  measured  by
 benchmarks to the speed of their processors, they often don't even mention the
 programming language and compiler used. In their detailed  documents,  usually
 called  "performance brief" or "performance report," they usually do give more
 details. However, these details are often lost in the press releases and other
 marketing  statements.  For serious performance evaluation, it is necessary to
 study the code generated by the various compilers.
 
 Dhrystone was originally published in Ada (Communications  of  the  ACM,  Oct.
 1984).  However, since good Ada compilers were rare at this time and, together
 with UNIX, C became more and more popular, the C version of Dhrystone  is  the
 one  now  mainly  used in industry. There are "official" versions 2.1 for Ada,
 Pascal, and C,  which  are  as  close  together  as  the  languages'  semantic
 differences permit.
 
 Dhrystone contains two statements  where  the  programming  language  and  its
 translation play a major part in the execution time measured by the benchmark:
 
   o   String assignment (in procedure Proc_0 / main)
   o   String comparison (in function Func_2)
 
 In Ada and Pascal, strings are arrays of characters where the  length  of  the
 string  is  part  of the type information known at compile time. In C, strings
 are also arrays of characters, but there  are  no  operators  defined  in  the
 language  for  assignment  and  comparison  of  strings.   Instead,  functions
 "strcpy" and "strcmp" are used. These functions are  defined  for  strings  of
 arbitrary  length, and make use of the fact that strings in C have to end with
 a terminating null byte. For general-purpose calls  to  these  functions,  the
 implementor  can  assume  nothing  about  the  length and the alignment of the
 strings involved.
 
 The C version of Dhrystone spends a relatively large amount of time  in  these
 two  functions.  Some  time  ago, I made measurements on a VAX 11/785 with the
 Berkeley UNIX (4.2) compilers (often-used compilers,  but  certainly  not  the
 most  advanced).  In  the  C  version, 23% of the time was spent in the string
 functions; in the Pascal version, only 10%. On good RISC machines (where  less
 time is spent in the procedure calling sequence than on a VAX) and with better
 optimizing compilers, the percentage is higher; MIPS has reported 34%  for  an
 R3000.   Because  of this effect, Pascal and Ada Dhrystone results are usually
 better than C results (except when the optimization quality of the C  compiler
 is considerably better than that of the other compilers).
 
 Several people have noted that the string operations are  over-represented  in
 Dhrystone,  mainly  because the strings occurring in Dhrystone are longer than
 average strings. I admit that this is true, and have said  so  in  my  SIGPLAN
 Notices  paper  (Aug.  1988);  however, I didn't want to generate confusion by
 changing the string lengths from version 1 to version 2.
 
 Even if they are somewhat over-represented in Dhrystone, string operations are
 frequent  enough  that  it makes sense to implement them in the most efficient
 way possible, not only for benchmarking purposes.  This means  that  they  can
 and should be written in assembly language code. ANSI C also explicitly allows
 the strings functions to be implemented as macros, i.e. by inline code.
 
 There is also a third way to speed up the "strcpy" statement in Dhrystone: For
 this  particular  "strcpy" statement, the source of the assignment is a string
 constant. Therefore, in contrast to calls to "strcpy" in the general case, the
 compiler  knows  the  length  and alignment of the strings involved at compile
 time and can generate code in the same efficient  way  as  a  Pascal  compiler
 (word instructions instead of byte instructions).
 
 This is not allowed in the case of the "strcmp" call: Here, the addresses  are
 formal  procedure  parameters, and no assumptions can be made about the length
 or alignment of the strings.  Any such assumptions would indicate an incorrect
 implementation.  They  might work for Dhrystone, where the strings are in fact
 word-aligned  with  typical  compilers,  but  other  programs  would   deliver
 incorrect results.
 
 So, for an apple-to-apple  comparison  between  processors,  and  not  between
 several  possible  (legal  or  illegal)  degrees of compiler optimization, one
 should check that the systems are comparable with  respect  to  the  following
 three points:
 
   (1) String functions in assembly language vs. in C
 
       Frequently used functions such as the string functions can and should be
       written  in  assembly language, and all serious C language systems known
       to me do this. (I list this point  for  completeness  only.)  Note  that
       processors  with an instruction that checks a word for a null byte (such
       as AMD's  29000  and  Intel's  80960)  have  an  advantage  here.  (This
       advantage  decreases  relatively if optimization (3) is applied.) Due to
       the length of the strings involved in Dhrystone, this advantage  may  be
       considered  too  high  in  perspective, but it is certainly legal to use
       such instructions - after all,  these  situations  are  what  they  were
       invented for.
 
   (2) String function code inline vs. as library functions.
 
       ANSI  C  has  created  a  new  situation,  compared   with   the   older
       Kernighan/Ritchie  C.  In  the  original C, the definition of the string
       function was not part of the  language.  Now  it  is,  and  inlining  is
       explicitly  allowed.  I  probably  should have stated more clearly in my
       SIGPLAN  Notices  paper  that  the  rule  "No  procedure  inlining   for
       Dhrystone"  referred  to  the  user level procedures only and not to the
       library routines.
 
   (3) Fixed-length and alignment assumptions for the strings
 
       Compilers should be allowed to optimize in these cases if (and only  if)
       it  is safe to do so. For Dhrystone, this is the "strcpy" statement, but
       not the  "strcmp"  statement  (unless,  of  course,  the  "strcmp"  code
       explicitly   checks   the  alignment  at  execution  time  and  branches
       accordingly).  A "Dhrystone switch" for the  compiler  that  causes  the
       generation  of  code  that  may  not work under certain circumstances is
       certainly inappropriate for comparisons. It has been reported in  Usenet
       that some C compilers provide such a compiler option; since I don't have
       access to all C compilers involved, I cannot verify this.
 
       If the fixed-length and word-alignment assumption can be  used,  a  wide
       bus  that permits fast multi-word load instructions certainly does help;
       however, this fact by itself should not make a really big difference.
 
 A check of  these  points  -  something  that  is  necessary  for  a  thorough
 evaluation  and  comparison  of  the  Dhrystone  performance claims - requires
 object code listings as well as listings for  the  string  functions  (strcpy,
 strcmp) that are possibly called by the program.
 
 I don't pretend that Dhrystone is  a  perfect  tool  to  measure  the  integer
 performance  of microprocessors. The more it is used and discussed, the more I
 myself learn about aspects that I hadn't noticed yet when I wrote the program.
 And  of  course,  the  very success of a benchmark program is a danger in that
 people may tune their compilers and/or hardware to it, and  with  this  action
 make it less useful.
 
 Whetstone and Linpack have their critical points also:  The  Whetstone  rating
 depends  heavily on the speed of the mathematical functions (sine, sqrt, ...),
 and Linpack is sensitive to data alignment for some cache configurations.
 
 Introduction of a standard set of public domain benchmark software  (something
 the  SPEC  effort attempts) is certainly a worthwhile thing.  In the meantime,
 people will continue to use whatever is available and widely distributed,  and
 Dhrystone  ratings  are probably still better than MIPS ratings if these are -
 as often in industry - based on  no  reproducible  derivation.   However,  any
 serious  performance  evaluation  requires  more than just a comparison of raw
 numbers; one has to make sure  that  the  numbers  have  been  obtained  in  a
 comparable way.

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