6.1.0570
>NUMBER
to-number
CORE
 
( ud1 c-addr1 u1 -- ud2 c-addr2 u2 )

ud2 is the unsigned result of converting the characters within the string specified by c-addr1 u1 into digits, using the number in BASE, and adding each into ud1 after multiplying ud1 by the number in BASE. Conversion continues left-to-right until a character that is not convertible, including any "+" or "-", is encountered or the string is entirely converted. c-addr2 is the location of the first unconverted character or the first character past the end of the string if the string was entirely converted. u2 is the number of unconverted characters in the string. An ambiguous condition exists if ud2 overflows during the conversion.

See:
3.2.1.2 Digit conversion.

Testing:
CREATE GN-BUF 0 C,
: GN-STRING GN-BUF 1 ;
: GN-CONSUMED GN-BUF CHAR+ 0 ;
: GN' [CHAR] ' WORD CHAR+ C@ GN-BUF C! GN-STRING ;

T{ 0 0 GN' 0' >NUMBER ->         0 0 GN-CONSUMED }T
T{ 0 0 GN' 1' >NUMBER ->         1 0 GN-CONSUMED }T
T{ 1 0 GN' 1' >NUMBER -> BASE @ 1+ 0 GN-CONSUMED }T
\ FOLLOWING SHOULD FAIL TO CONVERT
T{ 0 0 GN' -' >NUMBER ->         0 0 GN-STRING   }T
T{ 0 0 GN' +' >NUMBER ->         0 0 GN-STRING   }T
T{ 0 0 GN' .' >NUMBER ->         0 0 GN-STRING   }T

: >NUMBER-BASED
   BASE @ >R BASE ! >NUMBER R> BASE ! ;

T{ 0 0 GN' 2'       10 >NUMBER-BASED ->  2 0 GN-CONSUMED }T
T{ 0 0 GN' 2'        2 >NUMBER-BASED ->  0 0 GN-STRING   }T
T{ 0 0 GN' F'       10 >NUMBER-BASED ->  F 0 GN-CONSUMED }T
T{ 0 0 GN' G'       10 >NUMBER-BASED ->  0 0 GN-STRING   }T
T{ 0 0 GN' G' MAX-BASE >NUMBER-BASED -> 10 0 GN-CONSUMED }T
T{ 0 0 GN' Z' MAX-BASE >NUMBER-BASED -> 23 0 GN-CONSUMED }T

: GN1 ( UD BASE -- UD' LEN )
   \ UD SHOULD EQUAL UD' AND LEN SHOULD BE ZERO.
   BASE @ >R BASE !
   <# #S #>
   0 0 2SWAP >NUMBER SWAP DROP    \ RETURN LENGTH ONLY
   R> BASE ! ;

T{        0   0        2 GN1 ->        0   0 0 }T
T{ MAX-UINT   0        2 GN1 -> MAX-UINT   0 0 }T
T{ MAX-UINT DUP        2 GN1 -> MAX-UINT DUP 0 }T
T{        0   0 MAX-BASE GN1 ->        0   0 0 }T
T{ MAX-UINT   0 MAX-BASE GN1 -> MAX-UINT   0 0 }T
T{ MAX-UINT DUP MAX-BASE GN1 -> MAX-UINT DUP 0 }T