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mv src/lib to src/pkg
tests: all.bash passes, gobuild still works, godoc still works. R=rsc OCL=30096 CL=30102
This commit is contained in:
Rob Pike
parent
bf5c0c957c
commit
d90e7cbac6
391 changed files with 14 additions and 48 deletions
392
src/pkg/strconv/decimal.go
Normal file
392
src/pkg/strconv/decimal.go
Normal file
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Multiprecision decimal numbers.
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// For floating-point formatting only; not general purpose.
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// Only operations are assign and (binary) left/right shift.
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// Can do binary floating point in multiprecision decimal precisely
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// because 2 divides 10; cannot do decimal floating point
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// in multiprecision binary precisely.
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package strconv
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import "bytes"
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type decimal struct {
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// TODO(rsc): Can make d[] a bit smaller and add
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// truncated bool;
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d [2000] byte; // digits
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nd int; // number of digits used
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dp int; // decimal point
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};
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func (a *decimal) String() string;
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func (a *decimal) Assign(v uint64);
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func (a *decimal) Shift(k int) *decimal;
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func (a *decimal) Round(nd int) *decimal;
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func (a *decimal) RoundUp(nd int) *decimal;
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func (a *decimal) RoundDown(nd int) *decimal;
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func (a *decimal) RoundedInteger() uint64;
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func digitZero(dst []byte) int;
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func (a *decimal) String() string {
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n := 10 + a.nd;
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if a.dp > 0 {
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n += a.dp;
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}
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if a.dp < 0 {
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n += -a.dp;
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}
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buf := make([]byte, n);
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w := 0;
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switch {
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case a.nd == 0:
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return "0";
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case a.dp <= 0:
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// zeros fill space between decimal point and digits
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buf[w] = '0';
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w++;
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buf[w] = '.';
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w++;
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w += digitZero(buf[w:w+-a.dp]);
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w += bytes.Copy(buf[w:w+a.nd], a.d[0:a.nd]);
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case a.dp < a.nd:
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// decimal point in middle of digits
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w += bytes.Copy(buf[w:w+a.dp], a.d[0:a.dp]);
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buf[w] = '.';
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w++;
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w += bytes.Copy(buf[w:w+a.nd-a.dp], a.d[a.dp:a.nd]);
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default:
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// zeros fill space between digits and decimal point
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w += bytes.Copy(buf[w:w+a.nd], a.d[0:a.nd]);
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w += digitZero(buf[w:w+a.dp-a.nd]);
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}
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return string(buf[0:w]);
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}
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func copy(dst []byte, src []byte) int {
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for i := 0; i < len(dst); i++ {
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dst[i] = src[i];
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}
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return len(dst);
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}
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func digitZero(dst []byte) int {
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for i := 0; i < len(dst); i++ {
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dst[i] = '0';
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}
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return len(dst);
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}
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// trim trailing zeros from number.
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// (They are meaningless; the decimal point is tracked
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// independent of the number of digits.)
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func trim(a *decimal) {
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for a.nd > 0 && a.d[a.nd-1] == '0' {
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a.nd--;
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}
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if a.nd == 0 {
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a.dp = 0;
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}
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}
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// Assign v to a.
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func (a *decimal) Assign(v uint64) {
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var buf [50]byte;
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// Write reversed decimal in buf.
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n := 0;
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for v > 0 {
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v1 := v/10;
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v -= 10*v1;
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buf[n] = byte(v + '0');
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n++;
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v = v1;
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}
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// Reverse again to produce forward decimal in a.d.
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a.nd = 0;
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for n--; n>=0; n-- {
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a.d[a.nd] = buf[n];
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a.nd++;
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}
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a.dp = a.nd;
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trim(a);
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}
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func newDecimal(i uint64) *decimal {
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a := new(decimal);
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a.Assign(i);
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return a;
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}
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// Maximum shift that we can do in one pass without overflow.
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// Signed int has 31 bits, and we have to be able to accomodate 9<<k.
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const maxShift = 27
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// Binary shift right (* 2) by k bits. k <= maxShift to avoid overflow.
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func rightShift(a *decimal, k uint) {
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r := 0; // read pointer
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w := 0; // write pointer
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// Pick up enough leading digits to cover first shift.
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n := 0;
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for ; n>>k == 0; r++ {
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if r >= a.nd {
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if n == 0 {
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// a == 0; shouldn't get here, but handle anyway.
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a.nd = 0;
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return;
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}
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for n>>k == 0 {
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n = n*10;
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r++;
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}
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break;
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}
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c := int(a.d[r]);
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n = n*10 + c-'0';
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}
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a.dp -= r-1;
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// Pick up a digit, put down a digit.
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for ; r < a.nd; r++ {
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c := int(a.d[r]);
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dig := n>>k;
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n -= dig<<k;
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a.d[w] = byte(dig+'0');
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w++;
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n = n*10 + c-'0';
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}
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// Put down extra digits.
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for n > 0 {
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dig := n>>k;
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n -= dig<<k;
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a.d[w] = byte(dig+'0');
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w++;
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n = n*10;
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}
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a.nd = w;
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trim(a);
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}
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// Cheat sheet for left shift: table indexed by shift count giving
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// number of new digits that will be introduced by that shift.
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//
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// For example, leftcheats[4] = {2, "625"}. That means that
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// if we are shifting by 4 (multiplying by 16), it will add 2 digits
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// when the string prefix is "625" through "999", and one fewer digit
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// if the string prefix is "000" through "624".
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//
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// Credit for this trick goes to Ken.
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type leftCheat struct {
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delta int; // number of new digits
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cutoff string; // minus one digit if original < a.
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}
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var leftcheats = []leftCheat {
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// Leading digits of 1/2^i = 5^i.
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// 5^23 is not an exact 64-bit floating point number,
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// so have to use bc for the math.
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/*
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seq 27 | sed 's/^/5^/' | bc |
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awk 'BEGIN{ print "\tleftCheat{ 0, \"\" }," }
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{
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log2 = log(2)/log(10)
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printf("\tleftCheat{ %d, \"%s\" },\t// * %d\n",
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int(log2*NR+1), $0, 2**NR)
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}'
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*/
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leftCheat{ 0, "" },
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leftCheat{ 1, "5" }, // * 2
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leftCheat{ 1, "25" }, // * 4
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leftCheat{ 1, "125" }, // * 8
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leftCheat{ 2, "625" }, // * 16
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leftCheat{ 2, "3125" }, // * 32
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leftCheat{ 2, "15625" }, // * 64
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leftCheat{ 3, "78125" }, // * 128
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leftCheat{ 3, "390625" }, // * 256
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leftCheat{ 3, "1953125" }, // * 512
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leftCheat{ 4, "9765625" }, // * 1024
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leftCheat{ 4, "48828125" }, // * 2048
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leftCheat{ 4, "244140625" }, // * 4096
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leftCheat{ 4, "1220703125" }, // * 8192
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leftCheat{ 5, "6103515625" }, // * 16384
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leftCheat{ 5, "30517578125" }, // * 32768
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leftCheat{ 5, "152587890625" }, // * 65536
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leftCheat{ 6, "762939453125" }, // * 131072
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leftCheat{ 6, "3814697265625" }, // * 262144
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leftCheat{ 6, "19073486328125" }, // * 524288
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leftCheat{ 7, "95367431640625" }, // * 1048576
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leftCheat{ 7, "476837158203125" }, // * 2097152
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leftCheat{ 7, "2384185791015625" }, // * 4194304
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leftCheat{ 7, "11920928955078125" }, // * 8388608
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leftCheat{ 8, "59604644775390625" }, // * 16777216
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leftCheat{ 8, "298023223876953125" }, // * 33554432
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leftCheat{ 8, "1490116119384765625" }, // * 67108864
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leftCheat{ 9, "7450580596923828125" }, // * 134217728
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}
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// Is the leading prefix of b lexicographically less than s?
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func prefixIsLessThan(b []byte, s string) bool {
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for i := 0; i < len(s); i++ {
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if i >= len(b) {
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return true;
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}
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if b[i] != s[i] {
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return b[i] < s[i];
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}
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}
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return false;
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}
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// Binary shift left (/ 2) by k bits. k <= maxShift to avoid overflow.
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func leftShift(a *decimal, k uint) {
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delta := leftcheats[k].delta;
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if prefixIsLessThan(a.d[0:a.nd], leftcheats[k].cutoff) {
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delta--;
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}
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r := a.nd; // read index
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w := a.nd + delta; // write index
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n := 0;
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// Pick up a digit, put down a digit.
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for r--; r >= 0; r-- {
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n += (int(a.d[r])-'0') << k;
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quo := n/10;
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rem := n - 10*quo;
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w--;
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a.d[w] = byte(rem+'0');
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n = quo;
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}
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// Put down extra digits.
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for n > 0 {
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quo := n/10;
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rem := n - 10*quo;
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w--;
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a.d[w] = byte(rem+'0');
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n = quo;
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}
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if w != 0 {
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// TODO: Remove - has no business panicking.
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panicln("strconv: bad leftShift", w);
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}
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a.nd += delta;
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a.dp += delta;
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trim(a);
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}
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// Binary shift left (k > 0) or right (k < 0).
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// Returns receiver for convenience.
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func (a *decimal) Shift(k int) *decimal {
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switch {
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case a.nd == 0:
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// nothing to do: a == 0
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case k > 0:
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for k > maxShift {
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leftShift(a, maxShift);
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k -= maxShift;
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}
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leftShift(a, uint(k));
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case k < 0:
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for k < -maxShift {
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rightShift(a, maxShift);
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k += maxShift;
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}
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rightShift(a, uint(-k));
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}
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return a;
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}
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// If we chop a at nd digits, should we round up?
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func shouldRoundUp(a *decimal, nd int) bool {
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if nd <= 0 || nd >= a.nd {
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return false;
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}
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if a.d[nd] == '5' && nd+1 == a.nd { // exactly halfway - round to even
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return (a.d[nd-1] - '0') % 2 != 0;
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}
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// not halfway - digit tells all
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return a.d[nd] >= '5';
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}
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// Round a to nd digits (or fewer).
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// Returns receiver for convenience.
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func (a *decimal) Round(nd int) *decimal {
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if nd <= 0 || nd >= a.nd {
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return a;
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}
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if(shouldRoundUp(a, nd)) {
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return a.RoundUp(nd);
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}
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return a.RoundDown(nd);
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}
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// Round a down to nd digits (or fewer).
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// Returns receiver for convenience.
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func (a *decimal) RoundDown(nd int) *decimal {
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if nd <= 0 || nd >= a.nd {
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return a;
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}
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a.nd = nd;
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trim(a);
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return a;
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}
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// Round a up to nd digits (or fewer).
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// Returns receiver for convenience.
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func (a *decimal) RoundUp(nd int) *decimal {
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if nd <= 0 || nd >= a.nd {
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return a;
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}
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// round up
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for i := nd-1; i >= 0; i-- {
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c := a.d[i];
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if c < '9' { // can stop after this digit
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a.d[i]++;
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a.nd = i+1;
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return a;
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}
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}
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// Number is all 9s.
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// Change to single 1 with adjusted decimal point.
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a.d[0] = '1';
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a.nd = 1;
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a.dp++;
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return a;
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}
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// Extract integer part, rounded appropriately.
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// No guarantees about overflow.
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func (a *decimal) RoundedInteger() uint64 {
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if a.dp > 20 {
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return 0xFFFFFFFFFFFFFFFF;
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}
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var i int;
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n := uint64(0);
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for i = 0; i < a.dp && i < a.nd; i++ {
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n = n*10 + uint64(a.d[i] - '0');
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}
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for ; i < a.dp; i++ {
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n *= 10;
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}
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if shouldRoundUp(a, a.dp) {
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n++;
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}
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return n;
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}
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