An implementation of Unix dc and POSIX bc with GNU and BSD extensions
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4.3 KiB

Benchmarks

These are the results of benchmarks comparing this bc (at version 2.7.0) and GNU bc (at version 1.07.1), both compiled with clang 9 at -O2.

Note: all benchmarks were run four times, and the fastest run is the one shown. Also, [bc] means whichever bc was being run, and the assumed working directory is the root directory of this repository. Also, this bc was built at -O2.

Addition

The command used was:

tests/script.sh bc add.bc 1 0 1 1 [bc]

For GNU bc:

real 2.06
user 1.11
sys 0.95

For this bc:

real 0.98
user 0.95
sys 0.02

Subtraction

The command used was:

tests/script.sh bc subtract.bc 1 0 1 1 [bc]

For GNU bc:

real 2.04
user 1.04
sys 0.99

For this bc:

real 1.02
user 1.00
sys 0.01

Multiplication

The command used was:

tests/script.sh bc multiply.bc 1 0 1 1 [bc]

For GNU bc:

real 5.96
user 4.27
sys 1.68

For this bc:

real 2.15
user 2.11
sys 0.04

Division

The command used was:

tests/script.sh bc divide.bc 1 0 1 1 [bc]

For GNU bc:

real 2.74
user 1.84
sys 0.89

For this bc:

real 1.49
user 1.48
sys 0.00

Power

The command used was:

printf '1234567890^100000; halt\n' | time -p [bc] -lq > /dev/null

For GNU bc:

real 9.60
user 9.58
sys 0.01

For this bc:

real 0.67
user 0.66
sys 0.00

Scripts

This file was downloaded, saved at ../timeconst.bc and the following patch was applied:

--- ../timeconst.bc	2018-09-28 11:32:22.808669000 -0600
+++ ../timeconst.bc	2019-06-07 07:26:36.359913078 -0600
@@ -110,8 +110,10 @@
 
 		print "#endif /* KERNEL_TIMECONST_H */\n"
 	}
-	halt
 }
 
-hz = read();
-timeconst(hz)
+for (i = 0; i <= 50000; ++i) {
+	timeconst(i)
+}
+
+halt

The command used was:

time -p [bc] ../timeconst.bc > /dev/null

For GNU bc:

real 15.26
user 14.60
sys 0.64

For this bc:

real 11.24
user 11.23
sys 0.00

Because this bc is faster when doing math, it might be a better comparison to run a script that is not running any math. As such, I put the following into ../test.bc:

for (i = 0; i < 100000000; ++i) {
	y = i
}

i
y

halt

The command used was:

time -p [bc] ../test.bc > /dev/null

For GNU bc:

real 14.89
user 14.88
sys 0.00

For this bc:

real 22.19
user 22.18
sys 0.00

However, when I put the following into ../test2.bc:

i = 0

while (i < 100000000) {
	++i
}

i

halt

the results were surprising.

The command used was:

time -p [bc] ../test2.bc > /dev/null

For GNU bc:

real 42.92
user 32.70
sys 10.19

For this bc:

real 28.50
user 28.44
sys 0.02

I have no idea why the performance of both bc's fell off a cliff, especially the dismal showing by the GNU bc.

Note that, when running the benchmarks, the optimization used is not the one I recommend, which is -O3 -flto -march=native. This bc separates its code into modules that, when optimized at link time, removes a lot of the inefficiency that comes from function overhead. This is most keenly felt with one function: bc_vec_item(), which should turn into just one instruction (on x86_64) when optimized at link time and inlined. There are other functions that matter as well.

When compiling both bc's with the recommended optimizations, the results are as follows.

For the first script, the command was:

time -p [bc] ../timeconst.bc > /dev/null

For GNU bc:

real 14.01
user 13.41
sys 0.59

For this bc:

real 9.40
user 9.39
sys 0.00

For the second script, the command was:

time -p [bc] ../test.bc > /dev/null

For GNU bc:

real 12.58
user 12.58
sys 0.00

For this bc:

real 17.99
user 17.98
sys 0.00

For the third script, the command was:

time -p [bc] ../test2.bc > /dev/null

For GNU bc:

real 39.74
user 27.28
sys 12.44

For this bc:

real 23.31
user 23.27
sys 0.02

This is more competitive.

In addition, when compiling with the above recommendation, this bc gets even faster when doing math.

When I ran these benchmarks with my bc compiled under clang vs. gcc, it performed much better under clang. I recommend compiling this bc with clang.