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https://github.com/irmen/prog8.git
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56 lines
1.2 KiB
Lua
56 lines
1.2 KiB
Lua
%import textio
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%import floats
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%zeropage basicsafe
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; TODO fix VM : produces wrong number of primes (and varies too, so it uses uninitialized memory somewhere)
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main {
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const uword SIZE = 16000
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uword @zp flags_ptr = memory("flags", SIZE/8+1, $100)
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ubyte[] bitv = [ $01, $02, $04, $08, $10, $20, $40, $80 ]
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sub start() {
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txt.print("calculating... (expecting 3431): ")
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txt.print_uw(sieve())
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txt.print(" primes\n")
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}
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sub check_flag(uword idx) -> ubyte
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{
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ubyte mask = bitv[lsb(idx)&7]
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ubyte flag = flags_ptr[idx/8]
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return flag & mask
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}
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sub clear_flag(uword idx)
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{
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ubyte mask = bitv[lsb(idx)&7]
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ubyte flag = flags_ptr[idx/8]
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flag &= ~mask
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flags_ptr[idx/8] = flag
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}
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sub sieve() -> uword {
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uword prime
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uword k
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uword count=0
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uword i
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sys.memset(flags_ptr, SIZE/8+1, $ff)
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for i in 0 to SIZE-1 {
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if check_flag(i) {
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prime = i*2 + 3
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k = i + prime
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while k < SIZE {
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clear_flag(k)
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k += prime
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}
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count++
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}
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}
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return count
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}
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}
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