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Diffstat (limited to 'results/scraper/launchpad/1888165')
| -rw-r--r-- | results/scraper/launchpad/1888165 | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/results/scraper/launchpad/1888165 b/results/scraper/launchpad/1888165 new file mode 100644 index 000000000..fa3849313 --- /dev/null +++ b/results/scraper/launchpad/1888165 @@ -0,0 +1,21 @@ +loopz/loopnz clearing previous instruction's modified flags on cx -> 0 + +If you run QBasic in qemu, printing a double-type single-digit number will print an extra decimal point (e.g. PRINT CDBL(3) prints "3.") that does not appear when running on a real CPU (or on qemu with -enable-kvm). I tracked this down to the state of the status flags after a loopnz instruction. + +After executing a sequence like this in qemu: + + mov bx,1 + mov cx,1 + dec bx ; sets Z bit in flags +A: loopnz A ; should not modify flags + +Z is incorrectly clear afterwards. loopz does the same thing (but not plain loop). Interestingly, inserting pushf+popf after dec results in Z set, so loopnz/loopz does not always clear Z itself but is rather interfering with the previous instruction's flag setting. + +Version 5.1.0-rc0, x86-64 host. + + + + + +https://git.qemu.org/?p=qemu.git;a=commitdiff;h=3cb3a7720b01830abd5 + |