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+--- Thread: Why DEG? (/thread-22400.html)
Why DEG? - toml_12953 - 09-26-2024 10:19 AM
In the following Nqueens benchmark, why is DEG used after the ISG and DSE statements? There are no trig functions in the program. If they're supposed to be NOPs, why not just use a register increment or decrement? I'm confused.
Code:
LBL "NQUEENS"
TIME
STO "T0"
LBL A CLRG
8 STO 11
LBL 00 RCL 00 RCL 11
X=Y? GTO 04
ISG 00 DEG
STO IND 00
LBL 01 ISG 10 DEG
RCL 00 STO 09
LBL 02 DSE 09 DEG
RCL 09 X=0? GTO 00
RCL IND 00 RCL IND 09 -
X=0? GTO 03
ABS RCL 00 RCL 09 -
X<>Y? GTO 02
LBL 03 DSE IND 00 GTO 01
DSE 00 GTO 03
LBL 04 RCL 10
TIME
RCL "T0"
HMS-
→HR
3600
×
RTNRE: Why DEG? - rprosperi - 09-26-2024 11:55 AM
Just a guess, but I'd say DEG is being used as a NOP and it executes much faster than any register access or math operation, as it only sets some internal status bit(s).
RE: Why DEG? - Pekis - 09-26-2024 11:59 AM
(09-26-2024 11:55 AM)rprosperi Wrote: Just a guess, but I'd say DEG is being used as a NOP and it executes much faster than any register access or math operation, as it only sets some internal status bit(s).
... and there won't be any [useful]line skip after the ISG or DSE op
RE: Why DEG? - dmh - 09-26-2024 12:45 PM
It is used as a NOP.
I tried changing it to a synthetic NOP to see if it was much faster but it wasn't much different.
(09-26-2024 11:55 AM)rprosperi Wrote: Just a guess, but I'd say DEG is being used as a NOP and it executes much faster than any register access or math operation, as it only sets some internal status bit(s).
RE: Why DEG? - brouhaha - 09-26-2024 10:41 PM
(09-26-2024 10:19 AM)toml_12953 Wrote: If they're supposed to be NOPs, why not just use a register increment or decrement?
What specific instruction(s) are you suggesting for "register increment or decrement"? On most HP RPN calculators, ISG/DSE are the fastest register increment and decrement, and the only ones that don't affect the stack. Having to use a NOP of some sort after, if you don't use the conditional execution of the next line, is a small price to pay.
RE: Why DEG? - toml_12953 - 09-27-2024 12:36 AM
(09-26-2024 10:41 PM)brouhaha Wrote:(09-26-2024 10:19 AM)toml_12953 Wrote: If they're supposed to be NOPs, why not just use a register increment or decrement?
What specific instruction(s) are you suggesting for "register increment or decrement"? On most HP RPN calculators, ISG/DSE are the fastest register increment and decrement, and the only ones that don't affect the stack. Having to use a NOP of some sort after, if you don't use the conditional execution of the next line, is a small price to pay.
1
STO+ 00
or
1
STO- 00
RE: Why DEG? - xerxes - 09-27-2024 02:27 AM
(09-26-2024 10:19 AM)toml_12953 Wrote: In the following Nqueens benchmark, why is DEG used after the ISG and DSE statements?
Using ISG/DSE or ISZ/DSZ is a small optimization, because normally it's faster than 1 STO+/-.
As brouhaha stated, DEG (NOP) is necessary to suppress a skip.
RE: Why DEG? - Didier Lachieze - 09-27-2024 05:08 AM
(09-27-2024 12:36 AM)toml_12953 Wrote: 1
STO+ 00
or
1
STO- 00
This disturbs the stack by leaving 1 in X and T content is lost. So not a direct replacement for ISG 00 DEG or DSG 00 DEG.