diff options
Diffstat (limited to 'core')
| -rw-r--r-- | core/module-text.c | 29 | ||||
| -rw-r--r-- | core/test-module.c | 36 |
2 files changed, 65 insertions, 0 deletions
diff --git a/core/module-text.c b/core/module-text.c index 68c03b0..4ce1769 100644 --- a/core/module-text.c +++ b/core/module-text.c @@ -72,6 +72,35 @@ size_t pure_format_number(double value, char out[32]) { out[length] = 0; return length; } + /* The fewest decimals k whose digits, the value * 10^k rounded to the + * nearest integer m, read back as the value: %g's digits. m and 10^k are + * exact (m < 2^53, k <= 22), so m / 10^k is the correctly rounded value of + * those digits, as reading them is; the product's rounding error (fma) + * tells the nearest m, and a half between two goes to %g. Else, and for + * what %g would write with an exponent, the fewest %g digits that do. */ + static const double tens[] = {1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11, + 1e12, 1e13, 1e14, 1e15, 1e16}; + double magnitude = fabs(value); + if (magnitude >= 1e-4 && magnitude < 1e15) + for (int k = 1; k <= 16; ++k) { + double scaled = magnitude * tens[k]; + if (scaled >= 9007199254740992.0) break; + uint64_t m = (uint64_t)scaled; + double beyond = (scaled - (double)m) + fma(magnitude, tens[k], -scaled); + if (beyond == 0.5) break; + m += beyond > 0.5; + if ((double)m / tens[k] != magnitude) continue; + char digits[24]; + size_t count = 0, length = 0; + do { digits[count++] = (char)('0' + m % 10); m /= 10; } while (m); + while (count <= (size_t)k) digits[count++] = '0'; /* a leading zero before the point */ + if (value < 0) out[length++] = '-'; + while (count > (size_t)k) out[length++] = digits[--count]; + out[length++] = '.'; + while (count) out[length++] = digits[--count]; + out[length] = 0; + return length; + } for (int precision = 1; precision <= 17; ++precision) { snprintf(out, 32, "%.*g", precision, value); if (strtod(out, NULL) == value) break; diff --git a/core/test-module.c b/core/test-module.c index d5b7eee..8ca031c 100644 --- a/core/test-module.c +++ b/core/test-module.c @@ -3987,7 +3987,43 @@ static void timers(void) { CHECK(load(bad, &module_b) == PURE_INVALID && strstr(error, "view with an effect")); } +/* A number is written with the fewest digits that read back as it, the + * digits %g gives (with its exponent's leading zeros dropped): the same + * text as that search over precisions, for values of every kind. */ +static void number_texts(void) { + uint32_t seed = 0x6e756d73u; + size_t checked = 0; + for (unsigned i = 0; i < 300000; ++i) { + double value; + uint64_t bits = (uint64_t)next_random(&seed) << 32 | next_random(&seed); + switch (i % 5) { + case 0: value = (double)((int64_t)(bits % 2000001) - 1000000) / 100.0; break; /* money */ + case 1: value = (double)(bits % 20000001) / pow(10, (double)(bits >> 40 & 7)); break; /* decimals */ + case 2: memcpy(&value, &bits, sizeof(value)); if (!isfinite(value)) value = 0.75; break; + case 3: value = (double)(bits % 100000) / 7.0; break; + default: value = ldexp((double)(bits >> 11), (int)(bits % 80) - 60); break; + } + char got[32], want[32]; + pure_format_number(value, got); + if (value == 0) strcpy(want, "0"); + else if (value == floor(value) && fabs(value) < 1e15) snprintf(want, sizeof(want), "%.0f", value); + else { + for (int precision = 1; precision <= 17; ++precision) { + snprintf(want, sizeof(want), "%.*g", precision, value); + if (strtod(want, NULL) == value) break; + } + char *exponent = strchr(want, 'e'); + if (exponent) + while (exponent[2] == '0' && exponent[3]) memmove(exponent + 2, exponent + 3, strlen(exponent + 2)); + } + CHECK(!strcmp(got, want) && strtod(got, NULL) == value); + ++checked; + } + printf("{\"number_texts\":%zu}\n", checked); +} + int main(void) { + number_texts(); behaviour(); faults(); rejections(); |