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-rw-r--r--erts/emulator/sys/common/erl_sys_common_misc.c195
1 files changed, 111 insertions, 84 deletions
diff --git a/erts/emulator/sys/common/erl_sys_common_misc.c b/erts/emulator/sys/common/erl_sys_common_misc.c
index 1bf5fa89f4..5523b6fc0b 100644
--- a/erts/emulator/sys/common/erl_sys_common_misc.c
+++ b/erts/emulator/sys/common/erl_sys_common_misc.c
@@ -107,9 +107,9 @@ int erts_get_native_filename_encoding(void)
}
/* For internal use by sys_double_to_chars_fast() */
-static char* float_first_trailing_zero(char* p)
+static char* find_first_trailing_zero(char* p)
{
- for (--p; *p == '0' && *(p-1) == '0'; --p);
+ for (; *(p-1) == '0'; --p);
if (*(p-1) == '.') ++p;
return p;
}
@@ -120,34 +120,83 @@ sys_double_to_chars(double fp, char *buffer, size_t buffer_size)
return sys_double_to_chars_ext(fp, buffer, buffer_size, SYS_DEFAULT_FLOAT_DECIMALS);
}
+/* Convert float to string using fixed point notation.
+ * decimals must be >= 0
+ * if compact != 0, the trailing 0's will be truncated
+ */
int
-sys_double_to_chars_fast(double f, char *outbuf, int maxlen, int decimals, int compact)
+sys_double_to_chars_fast(double f, char *buffer, int buffer_size, int decimals, int compact)
{
- enum {
- FRAC_SIZE = 52
- , EXP_SIZE = 11
- , EXP_MASK = (1ll << EXP_SIZE) - 1
- , FRAC_MASK = (1ll << FRAC_SIZE) - 1
- , FRAC_MASK2 = (1ll << (FRAC_SIZE + 1)) - 1
- , MAX_FLOAT = 1ll << (FRAC_SIZE+1)
+ /* Note that some C compilers don't support "static const double" propagation into
+ * arrays so we use a define */
+ #define SYS_DOUBLE_RND_CONST 0.55555555555555555
+
+ static const double cs_sys_double_pow10[] = {
+ SYS_DOUBLE_RND_CONST / 1ll,
+ SYS_DOUBLE_RND_CONST / 10ll,
+ SYS_DOUBLE_RND_CONST / 100ll,
+ SYS_DOUBLE_RND_CONST / 1000ll,
+ SYS_DOUBLE_RND_CONST / 10000ll,
+ SYS_DOUBLE_RND_CONST / 100000ll,
+ SYS_DOUBLE_RND_CONST / 1000000ll,
+ SYS_DOUBLE_RND_CONST / 10000000ll,
+ SYS_DOUBLE_RND_CONST / 100000000ll,
+ SYS_DOUBLE_RND_CONST / 1000000000ll,
+ SYS_DOUBLE_RND_CONST / 10000000000ll,
+ SYS_DOUBLE_RND_CONST / 100000000000ll,
+ SYS_DOUBLE_RND_CONST / 1000000000000ll,
+ SYS_DOUBLE_RND_CONST / 10000000000000ll,
+ SYS_DOUBLE_RND_CONST / 100000000000000ll,
+ SYS_DOUBLE_RND_CONST / 1000000000000000ll,
+ SYS_DOUBLE_RND_CONST / 10000000000000000ll,
+ SYS_DOUBLE_RND_CONST / 100000000000000000ll,
+ SYS_DOUBLE_RND_CONST / 1000000000000000000ll
};
- long long mantissa, int_part, int_part2, frac_part;
+ static const int FRAC_SIZE = 52;
+ static const int EXP_SIZE = 11;
+ static const int EXP_MASK = (1ll << EXP_SIZE) - 1;
+ static const int MAX_DECIMALS = sizeof(cs_sys_double_pow10) / sizeof(cs_sys_double_pow10[0]);
+
+ static const long long FRAC_MASK = (1ll << FRAC_SIZE) - 1;
+ static const long long FRAC_MASK2 = (1ll << (FRAC_SIZE + 1)) - 1;
+ static const long long MAX_FLOAT = 1ll << (FRAC_SIZE+1);
+
+ long long mantissa, int_part = 0, frac_part = 0;
short exp;
- int sign, i, n, m, max;
- double absf;
+ int max;
+ int neg;
+ double fr;
union { long long L; double F; } x;
- char c, *p = outbuf;
- int digit, roundup;
+ char *p = buffer;
- x.F = f;
+ if (decimals < 0)
+ return -1;
+
+ /* Round the number to given decimal places. The number of 5's in the
+ * SYS_DOUBLE_RND_CONST constant is chosen such that adding any more 5's doesn't
+ * change the double precision of the number, i.e.:
+ * 1> term_to_binary(0.55555555555555555, [{minor_version, 1}]).
+ * <<131,70,63,225,199,28,113,199,28,114>>
+ * 2> term_to_binary(0.5555555555555555555, [{minor_version, 1}]).
+ * <<131,70,63,225,199,28,113,199,28,114>>
+ */
+ if (f >= 0) {
+ neg = 0;
+ fr = decimals < MAX_DECIMALS ? (f + cs_sys_double_pow10[decimals]) : f;
+ x.F = fr;
+ } else {
+ neg = 1;
+ fr = decimals < MAX_DECIMALS ? (f - cs_sys_double_pow10[decimals]) : f;
+ x.F = -fr;
+ }
exp = (x.L >> FRAC_SIZE) & EXP_MASK;
mantissa = x.L & FRAC_MASK;
- sign = x.L >= 0 ? 1 : -1;
+
if (exp == EXP_MASK) {
if (mantissa == 0) {
- if (sign == -1)
+ if (neg)
*p++ = '-';
*p++ = 'i';
*p++ = 'n';
@@ -158,101 +207,79 @@ sys_double_to_chars_fast(double f, char *outbuf, int maxlen, int decimals, int c
*p++ = 'n';
}
*p = '\0';
- return p - outbuf;
+ return p - buffer;
}
exp -= EXP_MASK >> 1;
mantissa |= (1ll << FRAC_SIZE);
- frac_part = 0;
- int_part = 0;
- absf = f * sign;
-
- /* Don't bother with optimizing too large numbers and decimals */
- if (absf > MAX_FLOAT || decimals > maxlen-17) {
- int len = erts_snprintf(outbuf, maxlen, "%.*f", decimals, f);
- if (len >= maxlen)
+
+ /* Don't bother with optimizing too large numbers or too large precision */
+ if (x.F > MAX_FLOAT || decimals >= MAX_DECIMALS) {
+ int len = erts_snprintf(buffer, buffer_size, "%.*f", decimals, f);
+ char* p = buffer + len;
+ if (len >= buffer_size)
return -1;
- p = outbuf + len;
/* Delete trailing zeroes */
if (compact)
- p = float_first_trailing_zero(outbuf + len);
+ p = find_first_trailing_zero(p);
*p = '\0';
- return p - outbuf;
- }
-
- if (exp >= FRAC_SIZE)
+ return p - buffer;
+ } else if (exp >= FRAC_SIZE) {
int_part = mantissa << (exp - FRAC_SIZE);
- else if (exp >= 0) {
+ } else if (exp >= 0) {
int_part = mantissa >> (FRAC_SIZE - exp);
frac_part = (mantissa << (exp + 1)) & FRAC_MASK2;
- }
- else /* if (exp < 0) */
+ } else /* if (exp < 0) */ {
frac_part = (mantissa & FRAC_MASK2) >> -(exp + 1);
+ }
- if (int_part == 0) {
- if (sign == -1)
+ if (!int_part) {
+ if (neg)
*p++ = '-';
*p++ = '0';
} else {
- int ret;
+ int ret, i, n;
while (int_part != 0) {
- int_part2 = int_part / 10;
- *p++ = (char)(int_part - ((int_part2 << 3) + (int_part2 << 1)) + '0');
- int_part = int_part2;
+ long long j = int_part / 10;
+ *p++ = (char)(int_part - ((j << 3) + (j << 1)) + '0');
+ int_part = j;
}
- if (sign == -1)
+ if (neg)
*p++ = '-';
/* Reverse string */
- ret = p - outbuf;
+ ret = p - buffer;
for (i = 0, n = ret/2; i < n; i++) {
- int j = ret - i - 1;
- c = outbuf[i];
- outbuf[i] = outbuf[j];
- outbuf[j] = c;
+ int j = ret - i - 1;
+ char c = buffer[i];
+ buffer[i] = buffer[j];
+ buffer[j] = c;
}
}
- if (decimals != 0)
+
+ if (decimals > 0) {
+ int i;
*p++ = '.';
- max = maxlen - (p - outbuf) - 1 /* leave room for trailing '\0' */;
- if (max > decimals)
+ max = buffer_size - (p - buffer) - 1 /* leave room for trailing '\0' */;
+
+ if (decimals > max)
+ return -1; /* the number is not large enough to fit in the buffer */
+
max = decimals;
- for (m = 0; m < max; m++) {
- /* frac_part *= 10; */
- frac_part = (frac_part << 3) + (frac_part << 1);
- *p++ = (char)((frac_part >> (FRAC_SIZE + 1)) + '0');
- frac_part &= FRAC_MASK2;
- }
+ for (i = 0; i < max; i++) {
+ /* frac_part *= 10; */
+ frac_part = (frac_part << 3) + (frac_part << 1);
- roundup = 0;
- /* Rounding - look at the next digit */
- frac_part = (frac_part << 3) + (frac_part << 1);
- digit = (frac_part >> (FRAC_SIZE + 1));
- if (digit > 5)
- roundup = 1;
- else if (digit == 5) {
- frac_part &= FRAC_MASK2;
- if (frac_part != 0) roundup = 1;
- }
- if (roundup) {
- char d;
- int pos = p - outbuf - 1;
- do {
- d = outbuf[pos];
- if (d == '-') break;
- if (d == '.') continue;
- if (++d != ':') {
- outbuf[pos] = d;
- break;
- }
- outbuf[pos] = '0';
- } while (--pos);
+ *p++ = (char)((frac_part >> (FRAC_SIZE + 1)) + '0');
+ frac_part &= FRAC_MASK2;
+ }
+
+ /* Delete trailing zeroes */
+ if (compact)
+ p = find_first_trailing_zero(p);
}
- /* Delete trailing zeroes */
- if (compact && *(p - 1) == '0')
- p = float_first_trailing_zero(--p);
*p = '\0';
- return p - outbuf;
+ return p - buffer;
}
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