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adler32 optimization #818

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This commit is contained in:
larshp 2017-07-08 11:07:10 +00:00
parent 5893634906
commit 2d9ef055d5
1 changed files with 16 additions and 3 deletions
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src/zabapgit_util.prog.abap
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@ -302,7 +302,8 @@ CLASS lcl_hash IMPLEMENTATION.
METHOD adler32.
CONSTANTS: lc_adler TYPE i VALUE 65521.
CONSTANTS: lc_adler TYPE i VALUE 65521,
lc_max_b TYPE i VALUE 1800000000.
DATA: lv_index TYPE i,
lv_a TYPE i VALUE 1,
@ -316,10 +317,22 @@ CLASS lcl_hash IMPLEMENTATION.
DO xstrlen( iv_xstring ) TIMES.
lv_index = sy-index - 1.
lv_a = ( lv_a + iv_xstring+lv_index(1) ) MOD lc_adler.
lv_b = ( lv_b + lv_a ) MOD lc_adler.
lv_a = lv_a + iv_xstring+lv_index(1).
lv_b = lv_b + lv_a.
* delay the MOD operation until the integer might overflow
* articles describe 5552 additions are allowed, but this assumes unsigned integers
* instead of allowing a fixed number of additions before running MOD, then
* just compare value of lv_b, this is 1 operation less than comparing and adding
IF lv_b > lc_max_b.
lv_a = lv_a MOD lc_adler.
lv_b = lv_b MOD lc_adler.
ENDIF.
ENDDO.
lv_a = lv_a MOD lc_adler.
lv_b = lv_b MOD lc_adler.
lv_x = lv_a.
lv_ca = lv_x.