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cpython/Objects/doubledigits.c
Christian Heimes 827b35c9fe Issue #1580: New free format floating point representation based on "Floating-Point Printer Sample Code", by Robert G. Burger. For example repr(11./5) now returns '2.2' instead of '2.2000000000000002'. 
Thanks to noam for the patch! I had to modify doubledigits.c slightly to support X64 and IA64 machines on Windows. I also added the new file to the three project files.
2007-12-10 22:19:17 +00:00

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/* Free-format floating point printer
*
* Based on "Floating-Point Printer Sample Code", by Robert G. Burger,
* http://www.cs.indiana.edu/~burger/fp/index.html
*/
#include "Python.h"
#if defined(__alpha) || defined(__i386) || defined(_M_IX86) || defined(_M_X64) || defined(_M_IA64)
#define LITTLE_ENDIAN_IEEE_DOUBLE
#elif !(defined(__ppc__) || defined(sparc) || defined(__sgi) || defined(_IBMR2) || defined(hpux))
#error unknown machine type
#endif
#if defined(_M_IX86)
#define UNSIGNED64 unsigned __int64
#elif defined(__alpha)
#define UNSIGNED64 unsigned long
#else
#define UNSIGNED64 unsigned long long
#endif
#ifndef U32
#define U32 unsigned int
#endif
/* exponent stored + 1024, hidden bit to left of decimal point */
#define bias 1023
#define bitstoright 52
#define m1mask 0xf
#define hidden_bit 0x100000
#ifdef LITTLE_ENDIAN_IEEE_DOUBLE
struct dblflt {
unsigned int m4: 16;
unsigned int m3: 16;
unsigned int m2: 16;
unsigned int m1: 4;
unsigned int e: 11;
unsigned int s: 1;
};
#else
/* Big Endian IEEE Double Floats */
struct dblflt {
unsigned int s: 1;
unsigned int e: 11;
unsigned int m1: 4;
unsigned int m2: 16;
unsigned int m3: 16;
unsigned int m4: 16;
};
#endif
#define float_radix 2.147483648e9
typedef UNSIGNED64 Bigit;
#define BIGSIZE 24
#define MIN_E -1074
#define MAX_FIVE 325
#define B_P1 ((Bigit)1 << 52)
typedef struct {
int l;
Bigit d[BIGSIZE];
} Bignum;
static Bignum R, S, MP, MM, five[MAX_FIVE];
static Bignum S2, S3, S4, S5, S6, S7, S8, S9;
static int ruf, k, s_n, use_mp, qr_shift, sl, slr;
static void mul10(Bignum *x);
static void big_short_mul(Bignum *x, Bigit y, Bignum *z);
/*
static void print_big(Bignum *x);
*/
static int estimate(int n);
static void one_shift_left(int y, Bignum *z);
static void short_shift_left(Bigit x, int y, Bignum *z);
static void big_shift_left(Bignum *x, int y, Bignum *z);
static int big_comp(Bignum *x, Bignum *y);
static int sub_big(Bignum *x, Bignum *y, Bignum *z);
static void add_big(Bignum *x, Bignum *y, Bignum *z);
static int add_cmp(void);
static int qr(void);
/*static int _PyFloat_Digits(char *buf, double v, int *signum);*/
/*static void _PyFloat_DigitsInit(void);*/
#define ADD(x, y, z, k) {\
Bigit x_add, z_add;\
x_add = (x);\
if ((k))\
z_add = x_add + (y) + 1, (k) = (z_add <= x_add);\
else\
z_add = x_add + (y), (k) = (z_add < x_add);\
(z) = z_add;\
}
#define SUB(x, y, z, b) {\
Bigit x_sub, y_sub;\
x_sub = (x); y_sub = (y);\
if ((b))\
(z) = x_sub - y_sub - 1, b = (y_sub >= x_sub);\
else\
(z) = x_sub - y_sub, b = (y_sub > x_sub);\
}
#define MUL(x, y, z, k) {\
Bigit x_mul, low, high;\
x_mul = (x);\
low = (x_mul & 0xffffffff) * (y) + (k);\
high = (x_mul >> 32) * (y) + (low >> 32);\
(k) = high >> 32;\
(z) = (low & 0xffffffff) | (high << 32);\
}
#define SLL(x, y, z, k) {\
Bigit x_sll = (x);\
(z) = (x_sll << (y)) | (k);\
(k) = x_sll >> (64 - (y));\
}
static void
mul10(Bignum *x)
{
int i, l;
Bigit *p, k;
l = x->l;
for (i = l, p = &x->d[0], k = 0; i >= 0; i--)
MUL(*p, 10, *p++, k);
if (k != 0)
*p = k, x->l = l+1;
}
static void
big_short_mul(Bignum *x, Bigit y, Bignum *z)
{
int i, xl, zl;
Bigit *xp, *zp, k;
U32 high, low;
xl = x->l;
xp = &x->d[0];
zl = xl;
zp = &z->d[0];
high = y >> 32;
low = y & 0xffffffff;
for (i = xl, k = 0; i >= 0; i--, xp++, zp++) {
Bigit xlow, xhigh, z0, t, c, z1;
xlow = *xp & 0xffffffff;
xhigh = *xp >> 32;
z0 = (xlow * low) + k; /* Cout is (z0 < k) */
t = xhigh * low;
z1 = (xlow * high) + t;
c = (z1 < t);
t = z0 >> 32;
z1 += t;
c += (z1 < t);
*zp = (z1 << 32) | (z0 & 0xffffffff);
k = (xhigh * high) + (c << 32) + (z1 >> 32) + (z0 < k);
}
if (k != 0)
*zp = k, zl++;
z->l = zl;
}
/*
static void
print_big(Bignum *x)
{
int i;
Bigit *p;
printf("#x");
i = x->l;
p = &x->d[i];
for (p = &x->d[i]; i >= 0; i--) {
Bigit b = *p--;
printf("%08x%08x", (int)(b >> 32), (int)(b & 0xffffffff));
}
}
*/
static int
estimate(int n)
{
if (n < 0)
return (int)(n*0.3010299956639812);
else
return 1+(int)(n*0.3010299956639811);
}
static void
one_shift_left(int y, Bignum *z)
{
int n, m, i;
Bigit *zp;
n = y / 64;
m = y % 64;
zp = &z->d[0];
for (i = n; i > 0; i--) *zp++ = 0;
*zp = (Bigit)1 << m;
z->l = n;
}
static void
short_shift_left(Bigit x, int y, Bignum *z)
{
int n, m, i, zl;
Bigit *zp;
n = y / 64;
m = y % 64;
zl = n;
zp = &(z->d[0]);
for (i = n; i > 0; i--) *zp++ = 0;
if (m == 0)
*zp = x;
else {
Bigit high = x >> (64 - m);
*zp = x << m;
if (high != 0)
*++zp = high, zl++;
}
z->l = zl;
}
static void
big_shift_left(Bignum *x, int y, Bignum *z)
{
int n, m, i, xl, zl;
Bigit *xp, *zp, k;
n = y / 64;
m = y % 64;
xl = x->l;
xp = &(x->d[0]);
zl = xl + n;
zp = &(z->d[0]);
for (i = n; i > 0; i--) *zp++ = 0;
if (m == 0)
for (i = xl; i >= 0; i--) *zp++ = *xp++;
else {
for (i = xl, k = 0; i >= 0; i--)
SLL(*xp++, m, *zp++, k);
if (k != 0)
*zp = k, zl++;
}
z->l = zl;
}
static int
big_comp(Bignum *x, Bignum *y)
{
int i, xl, yl;
Bigit *xp, *yp;
xl = x->l;
yl = y->l;
if (xl > yl) return 1;
if (xl < yl) return -1;
xp = &x->d[xl];
yp = &y->d[xl];
for (i = xl; i >= 0; i--, xp--, yp--) {
Bigit a = *xp;
Bigit b = *yp;
if (a > b) return 1;
else if (a < b) return -1;
}
return 0;
}
static int
sub_big(Bignum *x, Bignum *y, Bignum *z)
{
int xl, yl, zl, b, i;
Bigit *xp, *yp, *zp;
xl = x->l;
yl = y->l;
if (yl > xl) return 1;
xp = &x->d[0];
yp = &y->d[0];
zp = &z->d[0];
for (i = yl, b = 0; i >= 0; i--)
SUB(*xp++, *yp++, *zp++, b);
for (i = xl-yl; b && i > 0; i--) {
Bigit x_sub;
x_sub = *xp++;
*zp++ = x_sub - 1;
b = (x_sub == 0);
}
for (; i > 0; i--) *zp++ = *xp++;
if (b) return 1;
zl = xl;
while (*--zp == 0) zl--;
z->l = zl;
return 0;
}
static void
add_big(Bignum *x, Bignum *y, Bignum *z)
{
int xl, yl, k, i;
Bigit *xp, *yp, *zp;
xl = x->l;
yl = y->l;
if (yl > xl) {
int tl;
Bignum *tn;
tl = xl; xl = yl; yl = tl;
tn = x; x = y; y = tn;
}
xp = &x->d[0];
yp = &y->d[0];
zp = &z->d[0];
for (i = yl, k = 0; i >= 0; i--)
ADD(*xp++, *yp++, *zp++, k);
for (i = xl-yl; k && i > 0; i--) {
Bigit z_add;
z_add = *xp++ + 1;
k = (z_add == 0);
*zp++ = z_add;
}
for (; i > 0; i--) *zp++ = *xp++;
if (k)
*zp = 1, z->l = xl+1;
else
z->l = xl;
}
static int
add_cmp()
{
int rl, ml, sl, suml;
static Bignum sum;
rl = R.l;
ml = (use_mp ? MP.l : MM.l);
sl = S.l;
suml = rl >= ml ? rl : ml;
if ((sl > suml+1) || ((sl == suml+1) && (S.d[sl] > 1))) return -1;
if (sl < suml) return 1;
add_big(&R, (use_mp ? &MP : &MM), &sum);
return big_comp(&sum, &S);
}
static int
qr()
{
if (big_comp(&R, &S5) < 0)
if (big_comp(&R, &S2) < 0)
if (big_comp(&R, &S) < 0)
return 0;
else {
sub_big(&R, &S, &R);
return 1;
}
else if (big_comp(&R, &S3) < 0) {
sub_big(&R, &S2, &R);
return 2;
}
else if (big_comp(&R, &S4) < 0) {
sub_big(&R, &S3, &R);
return 3;
}
else {
sub_big(&R, &S4, &R);
return 4;
}
else if (big_comp(&R, &S7) < 0)
if (big_comp(&R, &S6) < 0) {
sub_big(&R, &S5, &R);
return 5;
}
else {
sub_big(&R, &S6, &R);
return 6;
}
else if (big_comp(&R, &S9) < 0)
if (big_comp(&R, &S8) < 0) {
sub_big(&R, &S7, &R);
return 7;
}
else {
sub_big(&R, &S8, &R);
return 8;
}
else {
sub_big(&R, &S9, &R);
return 9;
}
}
#define OUTDIG(d) { *buf++ = (d) + '0'; *buf = 0; return k; }
int
_PyFloat_Digits(char *buf, double v, int *signum)
{
struct dblflt *x;
int sign, e, f_n, m_n, i, d, tc1, tc2;
Bigit f;
/* decompose float into sign, mantissa & exponent */
x = (struct dblflt *)&v;
sign = x->s;
e = x->e;
f = (Bigit)(x->m1 << 16 | x->m2) << 32 | (U32)(x->m3 << 16 | x->m4);
if (e != 0) {
e = e - bias - bitstoright;
f |= (Bigit)hidden_bit << 32;
}
else if (f != 0)
/* denormalized */
e = 1 - bias - bitstoright;
*signum = sign;
if (f == 0) {
*buf++ = '0';
*buf = 0;
return 0;
}
ruf = !(f & 1); /* ruf = (even? f) */
/* Compute the scaling factor estimate, k */
if (e > MIN_E)
k = estimate(e+52);
else {
int n;
Bigit y;
for (n = e+52, y = (Bigit)1 << 52; f < y; n--) y >>= 1;
k = estimate(n);
}
if (e >= 0)
if (f != B_P1)
use_mp = 0, f_n = e+1, s_n = 1, m_n = e;
else
use_mp = 1, f_n = e+2, s_n = 2, m_n = e;
else
if ((e == MIN_E) || (f != B_P1))
use_mp = 0, f_n = 1, s_n = 1-e, m_n = 0;
else
use_mp = 1, f_n = 2, s_n = 2-e, m_n = 0;
/* Scale it! */
if (k == 0) {
short_shift_left(f, f_n, &R);
one_shift_left(s_n, &S);
one_shift_left(m_n, &MM);
if (use_mp) one_shift_left(m_n+1, &MP);
qr_shift = 1;
}
else if (k > 0) {
s_n += k;
if (m_n >= s_n)
f_n -= s_n, m_n -= s_n, s_n = 0;
else
f_n -= m_n, s_n -= m_n, m_n = 0;
short_shift_left(f, f_n, &R);
big_shift_left(&five[k-1], s_n, &S);
one_shift_left(m_n, &MM);
if (use_mp) one_shift_left(m_n+1, &MP);
qr_shift = 0;
}
else {
Bignum *power = &five[-k-1];
s_n += k;
big_short_mul(power, f, &S);
big_shift_left(&S, f_n, &R);
one_shift_left(s_n, &S);
big_shift_left(power, m_n, &MM);
if (use_mp) big_shift_left(power, m_n+1, &MP);
qr_shift = 1;
}
/* fixup */
if (add_cmp() <= -ruf) {
k--;
mul10(&R);
mul10(&MM);
if (use_mp) mul10(&MP);
}
/*
printf("\nk = %d\n", k);
printf("R = "); print_big(&R);
printf("\nS = "); print_big(&S);
printf("\nM- = "); print_big(&MM);
if (use_mp) printf("\nM+ = "), print_big(&MP);
putchar('\n');
fflush(0);
*/
if (qr_shift) {
sl = s_n / 64;
slr = s_n % 64;
}
else {
big_shift_left(&S, 1, &S2);
add_big(&S2, &S, &S3);
big_shift_left(&S2, 1, &S4);
add_big(&S4, &S, &S5);
add_big(&S4, &S2, &S6);
add_big(&S4, &S3, &S7);
big_shift_left(&S4, 1, &S8);
add_big(&S8, &S, &S9);
}
again:
if (qr_shift) { /* Take advantage of the fact that S = (ash 1 s_n) */
if (R.l < sl)
d = 0;
else if (R.l == sl) {
Bigit *p;
p = &R.d[sl];
d = *p >> slr;
*p &= ((Bigit)1 << slr) - 1;
for (i = sl; (i > 0) && (*p == 0); i--) p--;
R.l = i;
}
else {
Bigit *p;
p = &R.d[sl+1];
d = *p << (64 - slr) | *(p-1) >> slr;
p--;
*p &= ((Bigit)1 << slr) - 1;
for (i = sl; (i > 0) && (*p == 0); i--) p--;
R.l = i;
}
}
else /* We need to do quotient-remainder */
d = qr();
tc1 = big_comp(&R, &MM) < ruf;
tc2 = add_cmp() > -ruf;
if (!tc1)
if (!tc2) {
mul10(&R);
mul10(&MM);
if (use_mp) mul10(&MP);
*buf++ = d + '0';
goto again;
}
else
OUTDIG(d+1)
else
if (!tc2)
OUTDIG(d)
else {
big_shift_left(&R, 1, &MM);
if (big_comp(&MM, &S) == -1)
OUTDIG(d)
else
OUTDIG(d+1)
}
}
void
_PyFloat_DigitsInit()
{
int n, i, l;
Bignum *b;
Bigit *xp, *zp, k;
five[0].l = l = 0;
five[0].d[0] = 5;
for (n = MAX_FIVE-1, b = &five[0]; n > 0; n--) {
xp = &b->d[0];
b++;
zp = &b->d[0];
for (i = l, k = 0; i >= 0; i--)
MUL(*xp++, 5, *zp++, k);
if (k != 0)
*zp = k, l++;
b->l = l;
}
/*
for (n = 1, b = &five[0]; n <= MAX_FIVE; n++) {
big_shift_left(b++, n, &R);
print_big(&R);
putchar('\n');
}
fflush(0);
*/
}
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