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Diffstat (limited to 'theories/Init/Decimal.v')
-rw-r--r-- | theories/Init/Decimal.v | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/theories/Init/Decimal.v b/theories/Init/Decimal.v new file mode 100644 index 00000000..57163b1b --- /dev/null +++ b/theories/Init/Decimal.v @@ -0,0 +1,163 @@ +(************************************************************************) +(* * The Coq Proof Assistant / The Coq Development Team *) +(* v * INRIA, CNRS and contributors - Copyright 1999-2018 *) +(* <O___,, * (see CREDITS file for the list of authors) *) +(* \VV/ **************************************************************) +(* // * This file is distributed under the terms of the *) +(* * GNU Lesser General Public License Version 2.1 *) +(* * (see LICENSE file for the text of the license) *) +(************************************************************************) + +(** * Decimal numbers *) + +(** These numbers coded in base 10 will be used for parsing and printing + other Coq numeral datatypes in an human-readable way. + See the [Numeral Notation] command. + We represent numbers in base 10 as lists of decimal digits, + in big-endian order (most significant digit comes first). *) + +(** Unsigned integers are just lists of digits. + For instance, ten is (D1 (D0 Nil)) *) + +Inductive uint := + | Nil + | D0 (_:uint) + | D1 (_:uint) + | D2 (_:uint) + | D3 (_:uint) + | D4 (_:uint) + | D5 (_:uint) + | D6 (_:uint) + | D7 (_:uint) + | D8 (_:uint) + | D9 (_:uint). + +(** [Nil] is the number terminator. Taken alone, it behaves as zero, + but rather use [D0 Nil] instead, since this form will be denoted + as [0], while [Nil] will be printed as [Nil]. *) + +Notation zero := (D0 Nil). + +(** For signed integers, we use two constructors [Pos] and [Neg]. *) + +Inductive int := Pos (d:uint) | Neg (d:uint). + +Delimit Scope uint_scope with uint. +Bind Scope uint_scope with uint. +Delimit Scope int_scope with int. +Bind Scope int_scope with int. + +(** This representation favors simplicity over canonicity. + For normalizing numbers, we need to remove head zero digits, + and choose our canonical representation of 0 (here [D0 Nil] + for unsigned numbers and [Pos (D0 Nil)] for signed numbers). *) + +(** [nzhead] removes all head zero digits *) + +Fixpoint nzhead d := + match d with + | D0 d => nzhead d + | _ => d + end. + +(** [unorm] : normalization of unsigned integers *) + +Definition unorm d := + match nzhead d with + | Nil => zero + | d => d + end. + +(** [norm] : normalization of signed integers *) + +Definition norm d := + match d with + | Pos d => Pos (unorm d) + | Neg d => + match nzhead d with + | Nil => Pos zero + | d => Neg d + end + end. + +(** A few easy operations. For more advanced computations, use the conversions + with other Coq numeral datatypes (e.g. Z) and the operations on them. *) + +Definition opp (d:int) := + match d with + | Pos d => Neg d + | Neg d => Pos d + end. + +(** For conversions with binary numbers, it is easier to operate + on little-endian numbers. *) + +Fixpoint revapp (d d' : uint) := + match d with + | Nil => d' + | D0 d => revapp d (D0 d') + | D1 d => revapp d (D1 d') + | D2 d => revapp d (D2 d') + | D3 d => revapp d (D3 d') + | D4 d => revapp d (D4 d') + | D5 d => revapp d (D5 d') + | D6 d => revapp d (D6 d') + | D7 d => revapp d (D7 d') + | D8 d => revapp d (D8 d') + | D9 d => revapp d (D9 d') + end. + +Definition rev d := revapp d Nil. + +Module Little. + +(** Successor of little-endian numbers *) + +Fixpoint succ d := + match d with + | Nil => D1 Nil + | D0 d => D1 d + | D1 d => D2 d + | D2 d => D3 d + | D3 d => D4 d + | D4 d => D5 d + | D5 d => D6 d + | D6 d => D7 d + | D7 d => D8 d + | D8 d => D9 d + | D9 d => D0 (succ d) + end. + +(** Doubling little-endian numbers *) + +Fixpoint double d := + match d with + | Nil => Nil + | D0 d => D0 (double d) + | D1 d => D2 (double d) + | D2 d => D4 (double d) + | D3 d => D6 (double d) + | D4 d => D8 (double d) + | D5 d => D0 (succ_double d) + | D6 d => D2 (succ_double d) + | D7 d => D4 (succ_double d) + | D8 d => D6 (succ_double d) + | D9 d => D8 (succ_double d) + end + +with succ_double d := + match d with + | Nil => D1 Nil + | D0 d => D1 (double d) + | D1 d => D3 (double d) + | D2 d => D5 (double d) + | D3 d => D7 (double d) + | D4 d => D9 (double d) + | D5 d => D1 (succ_double d) + | D6 d => D3 (succ_double d) + | D7 d => D5 (succ_double d) + | D8 d => D7 (succ_double d) + | D9 d => D9 (succ_double d) + end. + +End Little. |