mirror of https://github.com/deater/tb1.git
58 lines
2.7 KiB
Plaintext
58 lines
2.7 KiB
Plaintext
Chart of size optimization
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Using gas 2.11.93.0.2
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goal = 8192 bytes
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Version Size (bytes) Notes
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~~~~~~~~ ~~~~~~~~~~~~~ ~~~~~~
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0.26 25422 First working version
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0.26 13260 Stripped
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0.27 13172 Removing extraneous spaces from strings
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0.27 11076 Compressed Data Segment
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0.28 8940 Removed ".data" line to force data+text in same segment
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0.28 8668 Using sstrip "super-strip"
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0.29 8656 move get_char to return status in carry flag
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1 byte immediate moves -> push/pop
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0.29 8620 make "blit_219"
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0.29 8592 Optimizing "do_story" routine to remove %bp use
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0.29 8556 Optimize "do_menu" to use lea
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0.29 8544 convert verify_quit to use zero flag result
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0.29 8528 convert check_inside to use carry flag for status
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0.29 8452 move sound_freq to one 32bit value rather than 16 f/d pair
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0.29 8448 optimize high score routines
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0.29 8440 change cmp $0/jl to just js
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0.30 8312 messing with new_game
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0.30 8283 more removal of bx->bp in new_game
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0.30 8231 cheat, have functions called at end of other functions instead have them follow and thus shave the end saving a call
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0.30 8228 remove extraneous phobos_sprite line
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0.30 8193 Messing with jmping midway into functions for code re-use
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0.30 8187 merging the ioctl commands ;)
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0.31 8151 fixing the game to work again, culling unneeded code
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0.32 8174 Added some game balancing stuff bloating it back up a bit
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I am guessing with further code manipulation could get another 100-200
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bytes off. But have become lazy.
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Why optimize for size? It makes you realize how wasteful high level
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code is even with optimizing compilers. Also on x86 optimizing for size is
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the same from 386 on up. Optimizing for speed is so convoluted you have to
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pick a particular generation of processor and even then it takes lots
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of tuning because speed can depent on other things such as cache hits.
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One nice thing about programs under 8k, they most likely fit in
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the icache entirely ;)
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Big lessons here. Function calls are killer! They take up 6 bytes!
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Avoid them whenever possible.
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Also, loading 32bit constants is also a pain. Also take 6 bytes!
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Not as bad as on RISC where can take up to 8 bytes. Luckily x86
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allows push imm/pop reg to load 8bit constant into 32 bit register
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in 3 bytes.
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Doing anything in memory rather than register is at least 6+ bytes!
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Not as bad as RISC where you must often load/modify/store (12bytes)
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but still a pain. Would possibly be mitigated if more registers
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available, but that would probably make code-size bigger to accomodate
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extra opcodes [waiting for x86-64 to see].
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