Newlib is a C standard library implementation (largely inspired by BSD libc) intended for use on embedded systems.
Apparently, the string to floating point conversion functions (strtod
, strtof
) use dynamic memory allocation by calling a function called Balloc
, which calls _calloc_r
which calls _malloc_r
.
Why?
I tried to look at the source code available online, but I couldn't make sense of it.
I found the call for the _Balloc
in the disassembly and tried many different inputs (strings) to try and trigger it getting called, but I didn't managed to get it called. (I can't trace the program in the C source code, as the library is precompiled (shared library) with heavy optimizations.)
I need to use a library that is full with calls to strtod
and the rest, so I can't easily eliminate these functions.
I don't have a heap on the microcontroller, I don't want to have a heap on the microcontroller, and I don't even have the _sbrk
function (which would ultimately be responsible for allocating the memory from the heap) implemented for me...
I now have only a stub for the _sbrk
which just triggers a hard fault if it gets called, so that the linker doesn't fail. But this is obviously not very good.
So I would like to know, why and when (what kind of input) will Balloc be called. Maybe I can prove that that type of input is impossible in my case so the stub would be a sanctionable hack.
Here is the strtod.c: https://www.codepile.net/pile/JZVLj6yQ
Edit:
_strtod_l() (this is what gets wrapped by strtod):
double
_strtod_l (struct _reent *ptr, const char *__restrict s00, char **__restrict se,
locale_t loc)
{
#ifdef Avoid_Underflow
int scale;
#endif
int bb2, bb5, bbe, bd2, bd5, bbbits, bs2, c, decpt, dsign,
e, e1, esign, i, j, k, nd, nd0, nf, nz, nz0, sign;
const char *s, *s0, *s1;
double aadj, adj;
U aadj1, rv, rv0;
Long L;
__ULong y, z;
_Bigint *bb = NULL, *bb1, *bd = NULL, *bd0, *bs = NULL, *delta = NULL;
#ifdef Avoid_Underflow
__ULong Lsb, Lsb1;
#endif
#ifdef SET_INEXACT
int inexact, oldinexact;
#endif
#ifdef Honor_FLT_ROUNDS
int rounding;
#endif
const char *decimal_point = __get_numeric_locale(loc)->decimal_point;
int dec_len = strlen (decimal_point);
delta = bs = bd = NULL;
sign = nz0 = nz = decpt = 0;
dval(rv) = 0.;
for(s = s00;;s++) switch(*s) {
case '-':
sign = 1;
/* no break */
case '+':
if (*++s)
goto break2;
/* no break */
case 0:
goto ret0;
case '\t':
case '\n':
case '\v':
case '\f':
case '\r':
case ' ':
continue;
default:
goto break2;
}
break2:
if (*s == '0') {
#ifndef NO_HEX_FP
{
static const FPI fpi = { 53, 1-1023-53+1, 2046-1023-53+1, 1, SI };
Long exp;
__ULong bits[2];
switch(s[1]) {
case 'x':
case 'X':
/* If the number is not hex, then the parse of
0 is still valid. */
s00 = s + 1;
{
#if defined(FE_DOWNWARD) && defined(FE_TONEAREST) && defined(FE_TOWARDZERO) && defined(FE_UPWARD)
FPI fpi1 = fpi;
switch(fegetround()) {
case FE_TOWARDZERO: fpi1.rounding = 0; break;
case FE_UPWARD: fpi1.rounding = 2; break;
case FE_DOWNWARD: fpi1.rounding = 3;
}
#else
#define fpi1 fpi
#endif
switch((i = gethex(ptr, &s, &fpi1, &exp, &bb, sign, loc)) & STRTOG_Retmask) {
case STRTOG_NoNumber:
s = s00;
sign = 0;
/* FALLTHROUGH */
case STRTOG_Zero:
break;
default:
if (bb) {
copybits(bits, fpi.nbits, bb);
Bfree(ptr,bb);
}
ULtod(rv.i, bits, exp, i);
}}
goto ret;
}
}
#endif
nz0 = 1;
while(*++s == '0') ;
if (!*s)
goto ret;
}
s0 = s;
y = z = 0;
for(nd = nf = 0; (c = *s) >= '0' && c <= '9'; nd++, s++)
if (nd < 9)
y = 10*y + c - '0';
else
z = 10*z + c - '0';
nd0 = nd;
if (strncmp (s, decimal_point, dec_len) == 0)
{
decpt = 1;
c = *(s += dec_len);
if (!nd) {
for(; c == '0'; c = *++s)
nz++;
if (c > '0' && c <= '9') {
s0 = s;
nf += nz;
nz = 0;
goto have_dig;
}
goto dig_done;
}
for(; c >= '0' && c <= '9'; c = *++s) {
have_dig:
nz++;
if (c -= '0') {
nf += nz;
for(i = 1; i < nz; i++)
if (nd++ < 9)
y *= 10;
else if (nd <= DBL_DIG + 1)
z *= 10;
if (nd++ < 9)
y = 10*y + c;
else if (nd <= DBL_DIG + 1)
z = 10*z + c;
nz = 0;
}
}
}
dig_done:
e = 0;
if (c == 'e' || c == 'E') {
if (!nd && !nz && !nz0) {
goto ret0;
}
s00 = s;
esign = 0;
switch(c = *++s) {
case '-':
esign = 1;
case '+':
c = *++s;
}
if (c >= '0' && c <= '9') {
while(c == '0')
c = *++s;
if (c > '0' && c <= '9') {
L = c - '0';
s1 = s;
while((c = *++s) >= '0' && c <= '9')
L = 10*L + c - '0';
if (s - s1 > 8 || L > 19999)
/* Avoid confusion from exponents
* so large that e might overflow.
*/
e = 19999; /* safe for 16 bit ints */
else
e = (int)L;
if (esign)
e = -e;
}
else
e = 0;
}
else
s = s00;
}
if (!nd) {
if (!nz && !nz0) {
#ifdef INFNAN_CHECK
/* Check for Nan and Infinity */
__ULong bits[2];
static const FPI fpinan = /* only 52 explicit bits */
{ 52, 1-1023-53+1, 2046-1023-53+1, 1, SI };
if (!decpt)
switch(c) {
case 'i':
case 'I':
if (match(&s,"nf")) {
--s;
if (!match(&s,"inity"))
++s;
dword0(rv) = 0x7ff00000;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
goto ret;
}
break;
case 'n':
case 'N':
if (match(&s, "an")) {
#ifndef No_Hex_NaN
if (*s == '(' /*)*/
&& hexnan(&s, &fpinan, bits)
== STRTOG_NaNbits) {
dword0(rv) = 0x7ff00000 | bits[1];
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = bits[0];
#endif /*!_DOUBLE_IS_32BITS*/
}
else {
#endif
dval(rv) = nan ("");
#ifndef No_Hex_NaN
}
#endif
goto ret;
}
}
#endif /* INFNAN_CHECK */
ret0:
s = s00;
sign = 0;
}
goto ret;
}
e1 = e -= nf;
/* Now we have nd0 digits, starting at s0, followed by a
* decimal point, followed by nd-nd0 digits. The number we're
* after is the integer represented by those digits times
* 10**e */
if (!nd0)
nd0 = nd;
k = nd < DBL_DIG + 1 ? nd : DBL_DIG + 1;
dval(rv) = y;
if (k > 9) {
#ifdef SET_INEXACT
if (k > DBL_DIG)
oldinexact = get_inexact();
#endif
dval(rv) = tens[k - 9] * dval(rv) + z;
}
bd0 = 0;
if (nd <= DBL_DIG
#ifndef RND_PRODQUOT
#ifndef Honor_FLT_ROUNDS
&& Flt_Rounds == 1
#endif
#endif
) {
if (!e)
goto ret;
if (e > 0) {
if (e <= Ten_pmax) {
#ifdef VAX
goto vax_ovfl_check;
#else
#ifdef Honor_FLT_ROUNDS
/* round correctly FLT_ROUNDS = 2 or 3 */
if (sign) {
dval(rv) = -dval(rv);
sign = 0;
}
#endif
/* rv = */ rounded_product(dval(rv), tens[e]);
goto ret;
#endif
}
i = DBL_DIG - nd;
if (e <= Ten_pmax + i) {
/* A fancier test would sometimes let us do
* this for larger i values.
*/
#ifdef Honor_FLT_ROUNDS
/* round correctly FLT_ROUNDS = 2 or 3 */
if (sign) {
dval(rv) = -dval(rv);
sign = 0;
}
#endif
e -= i;
dval(rv) *= tens[i];
#ifdef VAX
/* VAX exponent range is so narrow we must
* worry about overflow here...
*/
vax_ovfl_check:
dword0(rv) -= P*Exp_msk1;
/* rv = */ rounded_product(dval(rv), tens[e]);
if ((dword0(rv) & Exp_mask)
> Exp_msk1*(DBL_MAX_EXP+Bias-1-P))
goto ovfl;
dword0(rv) += P*Exp_msk1;
#else
/* rv = */ rounded_product(dval(rv), tens[e]);
#endif
goto ret;
}
}
#ifndef Inaccurate_Divide
else if (e >= -Ten_pmax) {
#ifdef Honor_FLT_ROUNDS
/* round correctly FLT_ROUNDS = 2 or 3 */
if (sign) {
dval(rv) = -dval(rv);
sign = 0;
}
#endif
/* rv = */ rounded_quotient(dval(rv), tens[-e]);
goto ret;
}
#endif
}
e1 += nd - k;
#ifdef IEEE_Arith
#ifdef SET_INEXACT
inexact = 1;
if (k <= DBL_DIG)
oldinexact = get_inexact();
#endif
#ifdef Avoid_Underflow
scale = 0;
#endif
#ifdef Honor_FLT_ROUNDS
if ((rounding = Flt_Rounds) >= 2) {
if (sign)
rounding = rounding == 2 ? 0 : 2;
else
if (rounding != 2)
rounding = 0;
}
#endif
#endif /*IEEE_Arith*/
/* Get starting approximation = rv * 10**e1 */
if (e1 > 0) {
if ( (i = e1 & 15) !=0)
dval(rv) *= tens[i];
if (e1 &= ~15) {
if (e1 > DBL_MAX_10_EXP) {
ovfl:
#ifndef NO_ERRNO
ptr->_errno = ERANGE;
#endif
/* Can't trust HUGE_VAL */
#ifdef IEEE_Arith
#ifdef Honor_FLT_ROUNDS
switch(rounding) {
case 0: /* toward 0 */
case 3: /* toward -infinity */
dword0(rv) = Big0;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = Big1;
#endif /*!_DOUBLE_IS_32BITS*/
break;
default:
dword0(rv) = Exp_mask;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
}
#else /*Honor_FLT_ROUNDS*/
dword0(rv) = Exp_mask;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
#endif /*Honor_FLT_ROUNDS*/
#ifdef SET_INEXACT
/* set overflow bit */
dval(rv0) = 1e300;
dval(rv0) *= dval(rv0);
#endif
#else /*IEEE_Arith*/
dword0(rv) = Big0;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = Big1;
#endif /*!_DOUBLE_IS_32BITS*/
#endif /*IEEE_Arith*/
if (bd0)
goto retfree;
goto ret;
}
e1 >>= 4;
for(j = 0; e1 > 1; j++, e1 >>= 1)
if (e1 & 1)
dval(rv) *= bigtens[j];
/* The last multiplication could overflow. */
dword0(rv) -= P*Exp_msk1;
dval(rv) *= bigtens[j];
if ((z = dword0(rv) & Exp_mask)
> Exp_msk1*(DBL_MAX_EXP+Bias-P))
goto ovfl;
if (z > Exp_msk1*(DBL_MAX_EXP+Bias-1-P)) {
/* set to largest number */
/* (Can't trust DBL_MAX) */
dword0(rv) = Big0;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = Big1;
#endif /*!_DOUBLE_IS_32BITS*/
}
else
dword0(rv) += P*Exp_msk1;
}
}
else if (e1 < 0) {
e1 = -e1;
if ( (i = e1 & 15) !=0)
dval(rv) /= tens[i];
if (e1 >>= 4) {
if (e1 >= 1 << n_bigtens)
goto undfl;
#ifdef Avoid_Underflow
if (e1 & Scale_Bit)
scale = 2*P;
for(j = 0; e1 > 0; j++, e1 >>= 1)
if (e1 & 1)
dval(rv) *= tinytens[j];
if (scale && (j = 2*P + 1 - ((dword0(rv) & Exp_mask)
>> Exp_shift)) > 0) {
/* scaled rv is denormal; zap j low bits */
if (j >= 32) {
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
if (j >= 53)
dword0(rv) = (P+2)*Exp_msk1;
else
dword0(rv) &= 0xffffffff << (j-32);
}
#ifndef _DOUBLE_IS_32BITS
else
dword1(rv) &= 0xffffffff << j;
#endif /*!_DOUBLE_IS_32BITS*/
}
#else
for(j = 0; e1 > 1; j++, e1 >>= 1)
if (e1 & 1)
dval(rv) *= tinytens[j];
/* The last multiplication could underflow. */
dval(rv0) = dval(rv);
dval(rv) *= tinytens[j];
if (!dval(rv)) {
dval(rv) = 2.*dval(rv0);
dval(rv) *= tinytens[j];
#endif
if (!dval(rv)) {
undfl:
dval(rv) = 0.;
#ifndef NO_ERRNO
ptr->_errno = ERANGE;
#endif
if (bd0)
goto retfree;
goto ret;
}
#ifndef Avoid_Underflow
#ifndef _DOUBLE_IS_32BITS
dword0(rv) = Tiny0;
dword1(rv) = Tiny1;
#else
dword0(rv) = Tiny1;
#endif /*_DOUBLE_IS_32BITS*/
/* The refinement below will clean
* this approximation up.
*/
}
#endif
}
}
/* Now the hard part -- adjusting rv to the correct value.*/
/* Put digits into bd: true value = bd * 10^e */
bd0 = s2b(ptr, s0, nd0, nd, y);
if (bd0 == NULL)
goto ovfl;
for(;;) {
bd = Balloc(ptr,bd0->_k);
if (bd == NULL)
goto ovfl;
Bcopy(bd, bd0);
bb = d2b(ptr,dval(rv), &bbe, &bbbits); /* rv = bb * 2^bbe */
if (bb == NULL)
goto ovfl;
bs = i2b(ptr,1);
if (bs == NULL)
goto ovfl;
if (e >= 0) {
bb2 = bb5 = 0;
bd2 = bd5 = e;
}
else {
bb2 = bb5 = -e;
bd2 = bd5 = 0;
}
if (bbe >= 0)
bb2 += bbe;
else
bd2 -= bbe;
bs2 = bb2;
#ifdef Honor_FLT_ROUNDS
if (rounding != 1)
bs2++;
#endif
#ifdef Avoid_Underflow
Lsb = LSB;
Lsb1 = 0;
j = bbe - scale;
i = j + bbbits - 1; /* logb(rv) */
j = P + 1 - bbbits;
if (i < Emin) { /* denormal */
i = Emin - i;
j -= i;
if (i < 32)
Lsb <<= i;
else
Lsb1 = Lsb << (i-32);
}
#else /*Avoid_Underflow*/
#ifdef Sudden_Underflow
#ifdef IBM
j = 1 + 4*P - 3 - bbbits + ((bbe + bbbits - 1) & 3);
#else
j = P + 1 - bbbits;
#endif
#else /*Sudden_Underflow*/
j = bbe;
i = j + bbbits - 1; /* logb(rv) */
if (i < Emin) /* denormal */
j += P - Emin;
else
j = P + 1 - bbbits;
#endif /*Sudden_Underflow*/
#endif /*Avoid_Underflow*/
bb2 += j;
bd2 += j;
#ifdef Avoid_Underflow
bd2 += scale;
#endif
i = bb2 < bd2 ? bb2 : bd2;
if (i > bs2)
i = bs2;
if (i > 0) {
bb2 -= i;
bd2 -= i;
bs2 -= i;
}
if (bb5 > 0) {
bs = pow5mult(ptr, bs, bb5);
if (bs == NULL)
goto ovfl;
bb1 = mult(ptr, bs, bb);
if (bb1 == NULL)
goto ovfl;
Bfree(ptr, bb);
bb = bb1;
}
if (bb2 > 0) {
bb = lshift(ptr, bb, bb2);
if (bb == NULL)
goto ovfl;
}
if (bd5 > 0) {
bd = pow5mult(ptr, bd, bd5);
if (bd == NULL)
goto ovfl;
}
if (bd2 > 0) {
bd = lshift(ptr, bd, bd2);
if (bd == NULL)
goto ovfl;
}
if (bs2 > 0) {
bs = lshift(ptr, bs, bs2);
if (bs == NULL)
goto ovfl;
}
delta = diff(ptr, bb, bd);
if (delta == NULL)
goto ovfl;
dsign = delta->_sign;
delta->_sign = 0;
i = cmp(delta, bs);
#ifdef Honor_FLT_ROUNDS
if (rounding != 1) {
if (i < 0) {
/* Error is less than an ulp */
if (!delta->_x[0] && delta->_wds <= 1) {
/* exact */
#ifdef SET_INEXACT
inexact = 0;
#endif
break;
}
if (rounding) {
if (dsign) {
adj = 1.;
goto apply_adj;
}
}
else if (!dsign) {
adj = -1.;
if (!dword1(rv)
&& !(dword0(rv) & Frac_mask)) {
y = dword0(rv) & Exp_mask;
#ifdef Avoid_Underflow
if (!scale || y > 2*P*Exp_msk1)
#else
if (y)
#endif
{
delta = lshift(ptr, delta,Log2P);
if (cmp(delta, bs) <= 0)
adj = -0.5;
}
}
apply_adj:
#ifdef Avoid_Underflow
if (scale && (y = dword0(rv) & Exp_mask)
<= 2*P*Exp_msk1)
dword0(adj) += (2*P+1)*Exp_msk1 - y;
#else
#ifdef Sudden_Underflow
if ((dword0(rv) & Exp_mask) <=
P*Exp_msk1) {
dword0(rv) += P*Exp_msk1;
dval(rv) += adj*ulp(dval(rv));
dword0(rv) -= P*Exp_msk1;
}
else
#endif /*Sudden_Underflow*/
#endif /*Avoid_Underflow*/
dval(rv) += adj*ulp(dval(rv));
}
break;
}
adj = ratio(delta, bs);
if (adj < 1.)
adj = 1.;
if (adj <= 0x7ffffffe) {
/* adj = rounding ? ceil(adj) : floor(adj); */
y = adj;
if (y != adj) {
if (!((rounding>>1) ^ dsign))
y++;
adj = y;
}
}
#ifdef Avoid_Underflow
if (scale && (y = dword0(rv) & Exp_mask) <= 2*P*Exp_msk1)
dword0(adj) += (2*P+1)*Exp_msk1 - y;
#else
#ifdef Sudden_Underflow
if ((dword0(rv) & Exp_mask) <= P*Exp_msk1) {
dword0(rv) += P*Exp_msk1;
adj *= ulp(dval(rv));
if (dsign)
dval(rv) += adj;
else
dval(rv) -= adj;
dword0(rv) -= P*Exp_msk1;
goto cont;
}
#endif /*Sudden_Underflow*/
#endif /*Avoid_Underflow*/
adj *= ulp(dval(rv));
if (dsign) {
if (dword0(rv) == Big0 && dword1(rv) == Big1)
goto ovfl;
dval(rv) += adj;
else
dval(rv) -= adj;
goto cont;
}
#endif /*Honor_FLT_ROUNDS*/
if (i < 0) {
/* Error is less than half an ulp -- check for
* special case of mantissa a power of two.
*/
if (dsign || dword1(rv) || dword0(rv) & Bndry_mask
#ifdef IEEE_Arith
#ifdef Avoid_Underflow
|| (dword0(rv) & Exp_mask) <= (2*P+1)*Exp_msk1
#else
|| (dword0(rv) & Exp_mask) <= Exp_msk1
#endif
#endif
) {
#ifdef SET_INEXACT
if (!delta->x[0] && delta->wds <= 1)
inexact = 0;
#endif
break;
}
if (!delta->_x[0] && delta->_wds <= 1) {
/* exact result */
#ifdef SET_INEXACT
inexact = 0;
#endif
break;
}
delta = lshift(ptr,delta,Log2P);
if (cmp(delta, bs) > 0)
goto drop_down;
break;
}
if (i == 0) {
/* exactly half-way between */
if (dsign) {
if ((dword0(rv) & Bndry_mask1) == Bndry_mask1
&& dword1(rv) == (
#ifdef Avoid_Underflow
(scale && (y = dword0(rv) & Exp_mask) <= 2*P*Exp_msk1)
? (0xffffffff & (0xffffffff << (2*P+1-(y>>Exp_shift)))) :
#endif
0xffffffff)) {
/*boundary case -- increment exponent*/
if (dword0(rv) == Big0 && dword1(rv) == Big1)
goto ovfl;
dword0(rv) = (dword0(rv) & Exp_mask)
+ Exp_msk1
#ifdef IBM
| Exp_msk1 >> 4
#endif
;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
#ifdef Avoid_Underflow
dsign = 0;
#endif
break;
}
}
else if (!(dword0(rv) & Bndry_mask) && !dword1(rv)) {
drop_down:
/* boundary case -- decrement exponent */
#ifdef Sudden_Underflow /*{{*/
L = dword0(rv) & Exp_mask;
#ifdef IBM
if (L < Exp_msk1)
#else
#ifdef Avoid_Underflow
if (L <= (scale ? (2*P+1)*Exp_msk1 : Exp_msk1))
#else
if (L <= Exp_msk1)
#endif /*Avoid_Underflow*/
#endif /*IBM*/
goto undfl;
L -= Exp_msk1;
#else /*Sudden_Underflow}{*/
#ifdef Avoid_Underflow
if (scale) {
L = dword0(rv) & Exp_mask;
if (L <= (2*P+1)*Exp_msk1) {
if (L > (P+2)*Exp_msk1)
/* round even ==> */
/* accept rv */
break;
/* rv = smallest denormal */
goto undfl;
}
}
#endif /*Avoid_Underflow*/
L = (dword0(rv) & Exp_mask) - Exp_msk1;
#endif /*Sudden_Underflow}*/
dword0(rv) = L | Bndry_mask1;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = 0xffffffff;
#endif /*!_DOUBLE_IS_32BITS*/
#ifdef IBM
goto cont;
#else
break;
#endif
}
#ifndef ROUND_BIASED
#ifdef Avoid_Underflow
if (Lsb1) {
if (!(dword0(rv) & Lsb1))
break;
}
else if (!(dword1(rv) & Lsb))
break;
#else
if (!(dword1(rv) & LSB))
break;
#endif
#endif
if (dsign)
#ifdef Avoid_Underflow
dval(rv) += sulp(rv, scale);
#else
dval(rv) += ulp(dval(rv));
#endif
#ifndef ROUND_BIASED
else {
#ifdef Avoid_Underflow
dval(rv) -= sulp(rv, scale);
#else
dval(rv) -= ulp(dval(rv));
#endif
#ifndef Sudden_Underflow
if (!dval(rv))
goto undfl;
#endif
}
#ifdef Avoid_Underflow
dsign = 1 - dsign;
#endif
#endif
break;
}
if ((aadj = ratio(delta, bs)) <= 2.) {
if (dsign)
aadj = dval(aadj1) = 1.;
else if (dword1(rv) || dword0(rv) & Bndry_mask) {
#ifndef Sudden_Underflow
if (dword1(rv) == Tiny1 && !dword0(rv))
goto undfl;
#endif
aadj = 1.;
dval(aadj1) = -1.;
}
else {
/* special case -- power of FLT_RADIX to be */
/* rounded down... */
if (aadj < 2./FLT_RADIX)
aadj = 1./FLT_RADIX;
else
aadj *= 0.5;
dval(aadj1) = -aadj;
}
}
else {
aadj *= 0.5;
dval(aadj1) = dsign ? aadj : -aadj;
#ifdef Check_FLT_ROUNDS
switch(Rounding) {
case 2: /* towards +infinity */
dval(aadj1) -= 0.5;
break;
case 0: /* towards 0 */
case 3: /* towards -infinity */
dval(aadj1) += 0.5;
}
#else
if (Flt_Rounds == 0)
dval(aadj1) += 0.5;
#endif /*Check_FLT_ROUNDS*/
}
y = dword0(rv) & Exp_mask;
/* Check for overflow */
if (y == Exp_msk1*(DBL_MAX_EXP+Bias-1)) {
dval(rv0) = dval(rv);
dword0(rv) -= P*Exp_msk1;
adj = dval(aadj1) * ulp(dval(rv));
dval(rv) += adj;
if ((dword0(rv) & Exp_mask) >=
Exp_msk1*(DBL_MAX_EXP+Bias-P)) {
if (dword0(rv0) == Big0 && dword1(rv0) == Big1)
goto ovfl;
dword0(rv) = Big0;
#ifndef _DOUBLE_IS_32BITS
dword1(rv) = Big1;
#endif /*!_DOUBLE_IS_32BITS*/
goto cont;
}
else
dword0(rv) += P*Exp_msk1;
}
else {
#ifdef Avoid_Underflow
if (scale && y <= 2*P*Exp_msk1) {
if (aadj <= 0x7fffffff) {
if ((z = aadj) == 0)
z = 1;
aadj = z;
dval(aadj1) = dsign ? aadj : -aadj;
}
dword0(aadj1) += (2*P+1)*Exp_msk1 - y;
}
adj = dval(aadj1) * ulp(dval(rv));
dval(rv) += adj;
#else
#ifdef Sudden_Underflow
if ((dword0(rv) & Exp_mask) <= P*Exp_msk1) {
dval(rv0) = dval(rv);
dword0(rv) += P*Exp_msk1;
adj = dval(aadj1) * ulp(dval(rv));
dval(rv) += adj;
#ifdef IBM
if ((dword0(rv) & Exp_mask) < P*Exp_msk1)
#else
if ((dword0(rv) & Exp_mask) <= P*Exp_msk1)
#endif
{
if (dword0(rv0) == Tiny0
&& dword1(rv0) == Tiny1)
goto undfl;
#ifndef _DOUBLE_IS_32BITS
dword0(rv) = Tiny0;
dword1(rv) = Tiny1;
#else
dword0(rv) = Tiny1;
#endif /*_DOUBLE_IS_32BITS*/
goto cont;
}
else
dword0(rv) -= P*Exp_msk1;
}
else {
adj = dval(aadj1) * ulp(dval(rv));
dval(rv) += adj;
}
#else /*Sudden_Underflow*/
/* Compute adj so that the IEEE rounding rules will
* correctly round rv + adj in some half-way cases.
* If rv * ulp(rv) is denormalized (i.e.,
* y <= (P-1)*Exp_msk1), we must adjust aadj to avoid
* trouble from bits lost to denormalization;
* example: 1.2e-307 .
*/
if (y <= (P-1)*Exp_msk1 && aadj > 1.) {
dval(aadj1) = (double)(int)(aadj + 0.5);
if (!dsign)
dval(aadj1) = -dval(aadj1);
}
adj = dval(aadj1) * ulp(dval(rv));
dval(rv) += adj;
#endif /*Sudden_Underflow*/
#endif /*Avoid_Underflow*/
}
z = dword0(rv) & Exp_mask;
#ifndef SET_INEXACT
#ifdef Avoid_Underflow
if (!scale)
#endif
if (y == z) {
/* Can we stop now? */
#ifndef _DOUBLE_IS_32BITS
/* If FE_INVALID floating point exceptions are
enabled, a conversion to a 32 bit value is
dangerous. A positive double value can result
in a negative 32 bit int, thus raising SIGFPE.
To avoid this, always convert into 64 bit here. */
__int64_t L = (__int64_t)aadj;
#else
L = (Long)aadj;
#endif
aadj -= L;
/* The tolerances below are conservative. */
if (dsign || dword1(rv) || dword0(rv) & Bndry_mask) {
if (aadj < .4999999 || aadj > .5000001)
break;
}
else if (aadj < .4999999/FLT_RADIX)
break;
}
#endif
cont:
Bfree(ptr,bb);
Bfree(ptr,bd);
Bfree(ptr,bs);
Bfree(ptr,delta);
}
#ifdef SET_INEXACT
if (inexact) {
if (!oldinexact) {
dword0(rv0) = Exp_1 + (70 << Exp_shift);
#ifndef _DOUBLE_IS_32BITS
dword1(rv0) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
dval(rv0) += 1.;
}
}
else if (!oldinexact)
clear_inexact();
#endif
#ifdef Avoid_Underflow
if (scale) {
dword0(rv0) = Exp_1 - 2*P*Exp_msk1;
#ifndef _DOUBLE_IS_32BITS
dword1(rv0) = 0;
#endif /*!_DOUBLE_IS_32BITS*/
dval(rv) *= dval(rv0);
#ifndef NO_ERRNO
/* try to avoid the bug of testing an 8087 register value */
if (dword0(rv) == 0 && dword1(rv) == 0)
ptr->_errno = ERANGE;
#endif
}
#endif /* Avoid_Underflow */
#ifdef SET_INEXACT
if (inexact && !(dword0(rv) & Exp_mask)) {
/* set underflow bit */
dval(rv0) = 1e-300;
dval(rv0) *= dval(rv0);
}
#endif
retfree:
Bfree(ptr,bb);
Bfree(ptr,bd);
Bfree(ptr,bs);
Bfree(ptr,bd0);
Bfree(ptr,delta);
ret:
if (se)
*se = (char *)s;
return sign ? -dval(rv) : dval(rv);
}
Why do strtod() and strtof() of the Newlib C Standard Library implementation uses dynamic memory allocation?
Leap of faith having not scanned the code: Because a quality conversion takes lots of space.
Consider DBL_MIN
takes hundreds of digits to convert to a string exactly. The next largest value also takes a similar amount of digits. A string nearly exactly half-way in between needs to examine these 100s of decimal digits, all the while forming a very long binary form in addition to the exponent it may have to multiply, in order return the best double
answer. Code is allocating based on its dynamic need.
If one is satisfied with a less-than-optimal conversion, only a few dozen bytes are needed for conversion to double
.
Choose your trade-offs: correctness, speed, size.
You can probably make a better fake version of _sbrk
. I'm not saying this is the best plan, but if it works ...
Give your program a nice global char heap[4096]
or whatever will fit, and a char *heap_ptr
and have your _sbrk
function use it.
User contributions licensed under CC BY-SA 3.0