Copilot commented on code in PR #4878:
URL: https://github.com/apache/arrow-adbc/pull/4878#discussion_r4244224458
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c/driver/sqlite/statement_reader.c:
##########
@@ -953,27 +953,30 @@ AdbcStatusCode
InternalSqliteStatementReaderAppendDoubleToBinary(
struct ArrowBuffer* offsets, struct ArrowBuffer* binary, double value,
int32_t* offset, struct AdbcError* error) {
static const size_t kReserve = 64;
- size_t buffer_size = kReserve;
- CHECK_NA(INTERNAL, ArrowBufferReserve(binary, buffer_size), error);
+ CHECK_NA(INTERNAL, ArrowBufferReserve(binary, kReserve), error);
char* output = (char*)(binary->data + binary->size_bytes);
- int written = 0;
- while (1) {
- written = snprintf(output, buffer_size, "%e", value);
- if (written < 0) {
- InternalAdbcSetError(error, "Encoding error when upcasting double to
string");
- return ADBC_STATUS_INTERNAL;
- } else if (((size_t)written) >= buffer_size) {
- // Truncated, resize and try again
- // Check for overflow - presumably this can never happen...?
- if (UINT_MAX - buffer_size < buffer_size) {
- InternalAdbcSetError(error, "Overflow when upcasting double to
string");
- return ADBC_STATUS_INTERNAL;
- }
- CHECK_NA(INTERNAL, ArrowBufferReserve(binary, buffer_size), error);
- buffer_size += buffer_size;
- continue;
+ // Keep enough significant digits to round-trip the binary64 value. SQLite's
+ // printf precision can be capped by the linked SQLite build, so use libc for
+ // finite values and SQLite's formatter for its non-finite spellings.
+ int written;
+ if (isfinite(value)) {
+ written = snprintf(output, (int)kReserve, "%.17g", value);
+ if (written >= 0 && written < (int)kReserve - 2 && strchr(output, '.') ==
NULL) {
Review Comment:
`snprintf("%.17g")` honors the process's `LC_NUMERIC`. With a decimal-comma
locale, a value such as `1.5` is written as `1,5`; the following
`strchr(output, '.')` then inserts `.0`, producing the invalid `1,5.0`. This
makes query output locale-dependent and breaks round-tripping. Please use a
locale-independent conversion (or safely normalize the locale decimal separator
before the `.0` logic) and cover a decimal-comma locale in the regression test.
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