From 9091e0fc630913999e3a51e860a2c4e07c6143c1 Mon Sep 17 00:00:00 2001 From: Sverker Eriksson Date: Fri, 16 Mar 2018 19:34:42 +0100 Subject: erts: Fix float_to_list(F, [{decimals,D}]) to better conform with io_lib:format("~.*f", [D,F]) --- erts/emulator/sys/common/erl_sys_common_misc.c | 184 +++++++++---------------- erts/emulator/test/num_bif_SUITE.erl | 25 ++++ 2 files changed, 91 insertions(+), 118 deletions(-) (limited to 'erts') diff --git a/erts/emulator/sys/common/erl_sys_common_misc.c b/erts/emulator/sys/common/erl_sys_common_misc.c index 96bdbacb9e..826307c077 100644 --- a/erts/emulator/sys/common/erl_sys_common_misc.c +++ b/erts/emulator/sys/common/erl_sys_common_misc.c @@ -142,7 +142,16 @@ 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. + +#if SIZEOF_LONG == 8 +# define round_int64 lround +#elif SIZEOF_LONG_LONG == 8 +# define round_int64 llround +#else +# error "No 64-bit integer type?" +#endif + +/* Convert float to string * decimals must be >= 0 * if compact != 0, the trailing 0's will be truncated */ @@ -154,80 +163,35 @@ sys_double_to_chars_fast(double f, char *buffer, int buffer_size, int decimals, #define FRAC_SIZE 52 #define EXP_SIZE 11 #define EXP_MASK (((Uint64)1 << EXP_SIZE) - 1) - #define MAX_DECIMALS (sizeof(cs_sys_double_pow10) \ - / sizeof(cs_sys_double_pow10[0])) + #define MAX_DECIMALS (sizeof(pow10v) / sizeof(pow10v[0])) #define FRAC_MASK (((Uint64)1 << FRAC_SIZE) - 1) #define FRAC_MASK2 (((Uint64)1 << (FRAC_SIZE + 1)) - 1) #define MAX_FLOAT ((Uint64)1 << (FRAC_SIZE+1)) - static const double cs_sys_double_pow10[] = { - SYS_DOUBLE_RND_CONST / 1e0, - SYS_DOUBLE_RND_CONST / 1e1, - SYS_DOUBLE_RND_CONST / 1e2, - SYS_DOUBLE_RND_CONST / 1e3, - SYS_DOUBLE_RND_CONST / 1e4, - SYS_DOUBLE_RND_CONST / 1e5, - SYS_DOUBLE_RND_CONST / 1e6, - SYS_DOUBLE_RND_CONST / 1e7, - SYS_DOUBLE_RND_CONST / 1e8, - SYS_DOUBLE_RND_CONST / 1e9, - SYS_DOUBLE_RND_CONST / 1e10, - SYS_DOUBLE_RND_CONST / 1e11, - SYS_DOUBLE_RND_CONST / 1e12, - SYS_DOUBLE_RND_CONST / 1e13, - SYS_DOUBLE_RND_CONST / 1e14, - SYS_DOUBLE_RND_CONST / 1e15, - SYS_DOUBLE_RND_CONST / 1e16, - SYS_DOUBLE_RND_CONST / 1e17, - SYS_DOUBLE_RND_CONST / 1e18 + static const double pow10v[] = { + 1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, + 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18 }; - Uint64 mantissa, int_part, frac_part; - int exp; - int fbits; - int max; + double af; + Uint64 int_part, frac_part; int neg; - double fr; - union { Uint64 L; double F; } x; char *p = buffer; if (decimals < 0) return -1; - if (f >= 0) { - neg = 0; - fr = decimals < MAX_DECIMALS ? (f + cs_sys_double_pow10[decimals]) : f; - x.F = fr; - } else { + if (f < 0) { neg = 1; - fr = decimals < MAX_DECIMALS ? (f - cs_sys_double_pow10[decimals]) : f; - x.F = -fr; + af = -f; } - - exp = (x.L >> FRAC_SIZE) & EXP_MASK; - mantissa = x.L & FRAC_MASK; - - if (exp == EXP_MASK) { - if (mantissa == 0) { - if (neg) - *p++ = '-'; - *p++ = 'i'; - *p++ = 'n'; - *p++ = 'f'; - } else { - *p++ = 'n'; - *p++ = 'a'; - *p++ = 'n'; - } - *p = '\0'; - return p - buffer; + else { + neg = 0; + af = f; } - exp -= EXP_MASK >> 1; - mantissa |= ((Uint64)1 << FRAC_SIZE); - /* Don't bother with optimizing too large numbers or too large precision */ - if (x.F > MAX_FLOAT || decimals >= MAX_DECIMALS) { + if (af > MAX_FLOAT || decimals >= MAX_DECIMALS) { int len = erts_snprintf(buffer, buffer_size, "%.*f", decimals, f); char* p = buffer + len; if (len >= buffer_size) @@ -237,77 +201,61 @@ sys_double_to_chars_fast(double f, char *buffer, int buffer_size, int decimals, p = find_first_trailing_zero(p); *p = '\0'; return p - buffer; - } else if (exp >= FRAC_SIZE) { - int_part = mantissa << (exp - FRAC_SIZE); - frac_part = 0; - fbits = FRAC_SIZE; /* not important as frac_part==0 */ - } else if (exp >= 0) { - fbits = FRAC_SIZE - exp; - int_part = mantissa >> fbits; - frac_part = mantissa & (((Uint64)1 << fbits) -1); - } else /* if (exp < 0) */ { - int_part = 0; - frac_part = mantissa; - fbits = FRAC_SIZE - exp; - } - - if (!int_part) { - if (neg) - *p++ = '-'; - *p++ = '0'; - } else { - int ret, i, n; - while (int_part != 0) { - *p++ = (char)((int_part % 10) + '0'); - int_part /= 10; - } - if (neg) - *p++ = '-'; - /* Reverse string */ - ret = p - buffer; - for (i = 0, n = ret/2; i < n; i++) { - int j = ret - i - 1; - char c = buffer[i]; - buffer[i] = buffer[j]; - buffer[j] = c; - } } - if (decimals > 0) { - int i; - *p++ = '.'; + if (decimals) { + double int_f = floor(af); + double frac_f = round((af - int_f) * pow10v[decimals]); - max = buffer_size - (p - buffer) - 1 /* leave room for trailing '\0' */; + int_part = (Uint64)int_f; + frac_part = (Uint64)frac_f; - if (decimals > max) - return -1; /* the number is not large enough to fit in the buffer */ - - max = decimals; + if (frac_f >= pow10v[decimals]) { + /* rounding overflow carry into int_part */ + int_part++; + frac_part = 0; + } - for (i = 0; i < max; i++) { - if (frac_part > (ERTS_UINT64_MAX/5)) { - frac_part >>= 3; - fbits -= 3; + do { + if (!frac_part) { + do { + *p++ = '0'; + } while (--decimals); + break; } + *p++ = (char)((frac_part % 10) + '0'); + frac_part /= 10; + } while (--decimals); - /* Multiply by 10 (5*2) to extract decimal digit as integer part */ - frac_part *= 5; - fbits--; + *p++ = '.'; + } + else + int_part = (Uint64)round_int64(af); - if (fbits >= 64) { - *p++ = '0'; - } - else { - *p++ = (char)((frac_part >> fbits) + '0'); - frac_part &= ((Uint64)1 << fbits) - 1; - } + if (!int_part) { + *p++ = '0'; + } else { + do { + *p++ = (char)((int_part % 10) + '0'); + int_part /= 10; + }while (int_part); + } + if (neg) + *p++ = '-'; + + {/* Reverse string */ + int i = 0; + int j = p - buffer - 1; + for ( ; i < j; i++, j--) { + char tmp = buffer[i]; + buffer[i] = buffer[j]; + buffer[j] = tmp; } - - /* Delete trailing zeroes */ - if (compact) - p = find_first_trailing_zero(p); } + /* Delete trailing zeroes */ + if (compact) + p = find_first_trailing_zero(p); *p = '\0'; return p - buffer; } diff --git a/erts/emulator/test/num_bif_SUITE.erl b/erts/emulator/test/num_bif_SUITE.erl index 592542405f..104bd37817 100644 --- a/erts/emulator/test/num_bif_SUITE.erl +++ b/erts/emulator/test/num_bif_SUITE.erl @@ -213,6 +213,20 @@ fts_rand_float_decimals(N) -> [begin F0 = rand_float_reasonable(), L0 = float_to_list(F0, [{decimals, D}]), + case conform_with_io_lib_format(F0,D) of + false -> ok; + true -> + IOL = lists:flatten(io_lib:format("~.*f", [D, F0])), + true = case L0 =:= IOL of + true -> true; + false -> + io:format("F0 = ~w ~w\n", [F0, <>]), + io:format("decimals = ~w\n", [D]), + io:format("float_to_list = ~s\n", [L0]), + io:format("io_lib:format = ~s\n", [IOL]), + false + end + end, L1 = case D of 0 -> L0 ++ ".0"; _ -> L0 @@ -234,6 +248,17 @@ fts_rand_float_decimals(N) -> fts_rand_float_decimals(N-1). +conform_with_io_lib_format(_, 0) -> + %% io_lib:format("~.*f") does not support zero decimals + false; +conform_with_io_lib_format(_, D) when D > 10 -> + %% Seems float_to_list gets it slightly wrong sometimes for many decimals + false; +conform_with_io_lib_format(F, D) -> + %% io_lib:format prints '0' for input bits beyond mantissa precision + %% float_to_list treats those unknown input bits as if they were zeros. + math:log2(abs(F) * math:pow(10,D)) < 54. + max_diff_decimals(F, D) -> IntBits = floor(math:log2(abs(F))) + 1, FracBits = (52 - IntBits), -- cgit v1.2.3