Sieve of Eratosthenes: Difference between revisions
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====using 'easy way' to 'add' 2n wheels==== |
====using 'easy way' to 'add' 2n wheels==== |
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{{trans|ZX Spectrum Basic}} |
{{trans|ZX Spectrum Basic}} |
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Sets h$ to 1 for higher multiples of 2 via <code>FILL$</code>, later on |
Sets h$ to 1 for higher multiples of 2 via <code>FILL$</code>, later on augments each <code>STEP</code> accordingly; replaces Floating Pt array p(z) with string variable h$(z) to sieve out all primes < z=441 (<code>l</code>=21) in under 1K, so that h$ is fillable to its maximum (32766), even on a 48K ZX Spectrum if translated back. |
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<lang qbasic> |
<lang qbasic> |
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10 INPUT "Enter Stopping Pt for squared factors: ";z |
10 INPUT "Enter Stopping Pt for squared factors: ";z |
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15 LET l=SQR(z) |
15 LET l=SQR(z) |
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20 LET h$="10" : h$=h$ & FILL$("01",z) |
20 LET h$="10" : h$=h$ & FILL$("01",z) |
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40 FOR n=3 TO l |
40 FOR n=3 TO l STEP 2 |
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50 IF h$(n) THEN NEXT n |
50 IF h$(n) THEN NEXT n |
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60 FOR k=n*n TO z STEP n+n: h$(k)=1 |
60 FOR k=n*n TO z STEP n+n: h$(k)=1 |
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====2i wheel emulation of Sinclair ZX81 BASIC==== |
====2i wheel emulation of Sinclair ZX81 BASIC==== |
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Backward-compatible also on Spectrums, as well as 1K ZX81s for all primes < Z=441. N.B. |
Backward-compatible also on Spectrums, as well as 1K ZX81s for all primes < Z=441. N.B. the <code>STEP</code> of 2 in line 40 mitigates line 50's inefficiency when going to 90. <lang qbasic> |
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10 INPUT Z |
10 INPUT Z |
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15 LET L=SQR(Z) |
15 LET L=SQR(Z) |
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