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truncating of float constants when

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used in float64 or float32 contexts

R=r
OCL=20297
CL=20297
This commit is contained in:
Ken Thompson 2008-12-02 17:03:47 -08:00
parent acfd1fd443
commit 89996e1fb1
2 changed files with 46 additions and 22 deletions
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53
src/cmd/gc/const.c
View File

@ -5,6 +5,34 @@
#include "go.h"
#define TUP(x,y) (((x)<<16)|(y))
void
truncfltlit(Mpflt *fv, Type *t)
{
double d;
float f;
if(t == T)
return;
// convert large precision literal floating
// into limited precision (float64 or float32)
// botch -- this assumes that compiler fp
// has same precision as runtime fp
switch(t->etype) {
case TFLOAT64:
d = mpgetflt(fv);
mpmovecflt(fv, d);
break;
case TFLOAT32:
d = mpgetflt(fv);
f = d;
d = f;
mpmovecflt(fv, d);
break;
}
}
void
convlit(Node *n, Type *t)
{
@ -90,15 +118,18 @@ convlit(Node *n, Type *t)
if(isfloat[et]) {
// int to float
Mpint *xv;
Mpflt *fv;
xv = n->val.u.xval;
if(mpcmpfixflt(xv, minfltval[et]) < 0)
goto bad2;
if(mpcmpfixflt(xv, maxfltval[et]) > 0)
goto bad2;
n->val.u.fval = mal(sizeof(*n->val.u.fval));
mpmovefixflt(n->val.u.fval, xv);
fv = mal(sizeof(*n->val.u.fval));
n->val.u.fval = fv;
mpmovefixflt(fv, xv);
n->val.ctype = CTFLT;
truncfltlit(fv, t);
break;
}
goto bad1;
@ -126,8 +157,6 @@ convlit(Node *n, Type *t)
}
if(isfloat[et]) {
// float to float
double d;
float f;
Mpflt *fv;
fv = n->val.u.fval;
@ -135,24 +164,13 @@ convlit(Node *n, Type *t)
goto bad2;
if(mpcmpfltflt(fv, maxfltval[et]) > 0)
goto bad2;
// switch(et) {
// case TFLOAT64:
// d = mpgetflt(fv);
// mpmovecflt(fv, d);
// break;
//
// case TFLOAT32:
// d = mpgetflt(fv);
// f = d;
// d = f;
// mpmovecflt(fv, d);
// break;
// }
truncfltlit(fv, t);
break;
}
goto bad1;
}
n->type = t;
return;
bad1:
@ -442,6 +460,7 @@ ret:
} else
if(wl == Wlitfloat) {
n->val.u.fval = fval;
truncfltlit(fval, n->type);
}
}

15
src/cmd/gc/mparith3.c
View File

@ -176,11 +176,15 @@ mpgetflt(Mpflt *a)
mpnorm(a);
}
while((a->val.a[Mpnorm-1] & (1L<<(Mpscale-1))) == 0) {
while((a->val.a[Mpnorm-1] & Mpsign) == 0) {
mpshiftfix(&a->val, 1);
a->exp -= 1;
}
// the magic numbers (64, 63, 53, 10) are
// IEEE specific. this should be done machine
// independently or in the 6g half of the compiler
// pick up the mantissa in a uvlong
s = 63;
v = 0;
@ -191,13 +195,14 @@ mpgetflt(Mpflt *a)
if(s > 0)
v = (v<<s) | (a->val.a[i]>>(Mpscale-s));
// should do this in multi precision
// 63 bits of mantissa being rounded to 53
// should do this in multi precision
if((v&0x3ffULL) != 0x200ULL || (v&0x400) != 0)
v += 0x200ULL; // round
v &= ~0x3ffULL;
v += 0x200ULL; // round toward even
v >>= 10;
f = (double)(v);
f = ldexp(f, Mpnorm*Mpscale + a->exp - 63);
f = ldexp(f, Mpnorm*Mpscale + a->exp - 53);
if(a->val.neg)
f = -f;