gbdev/rgbds
1
0
Fork 0
mirror of https://github.com/gbdev/rgbds.git synced 2025-11-20 10:12:06 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fix the FOR loop count formula (#1222)

Browse Source
This commit is contained in:
Rangi
2023-11-07 17:43:46 -05:00
committed by GitHub
parent 5379e51094
commit 9fc088dcb0
4 changed files with 46 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
test/asm/for-loop-count.asm Normal file
View File

@@ -0,0 +1,19 @@
; `FOR value, start, stop, step` calculates an initial count of loop repetitions as follows:
; - if (step > 0 && start < stop) then count = (stop - start - 1) / step + 1
; - if (step < 0 && stop < start) then count = (start - stop - 1) / -step + 1
; - else count = 0
; The absolute vaue |stop - start| needs to be 64-bit for this formula to work.
; Results may be compared with Python range(start, stop, step).
MACRO test
PRINTLN STRFMT("FOR x, %d, %d, %d", \1, \2, \3)
FOR x, \1, \2, \3
PRINTLN " {08x:x} = {d:x}"
ENDR
PRINTLN " done {08x:x} = {d:x}"
ENDM
test $8000_0000, $6000_0000, $4000_0000 ; [-2147483648, -1073741824, 0, 1073741824]
test $8000_0000, $7000_0000, $4400_0000 ; [-2147483648, -1006632960, 134217728, 1275068416]
test $7fff_ffff, $8000_0000, $8000_0000 ; [2147483647, -1]
test $8000_0000, $ffff_ffff, $8000_0000 ; []