RosettaCodeData/Task/Digital-root/PARI-GP/digital-root.pari

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dsum(n)=my(s); while(n, s+=n%10; n\=10); s
additivePersistence(n)=my(s); while(n>9, s++; n=dsum(n)); s
digitalRoot(n)=if(n, (n-1)%9+1, 0)
	`dsum(n)=my(s); while(n, s+=n%10; n\=10); s`
	`additivePersistence(n)=my(s); while(n>9, s++; n=dsum(n)); s`
	`digitalRoot(n)=if(n, (n-1)%9+1, 0)`