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Adding comments.

This commit is contained in:
Daniel Lemire 2020-03-16 20:17:48 -04:00
parent 032936a7b5
commit 0164723a8e
1 changed files with 7 additions and 3 deletions
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10
src/generic/numberparsing.h
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@ -10,6 +10,9 @@ namespace numberparsing {
really_inline double compute_float_64(int64_t power, uint64_t i, bool negative,
bool *success) {
// we start with a fast path
// It was described in
// Clinger WD. How to read floating point numbers accurately.
// ACM SIGPLAN Notices. 1990
if (-22 <= power && power <= 22 && i <= 9007199254740991) {
// convert the integer into a double. This is lossless since
// 0 <= i <= 2^53 - 1.
@ -35,10 +38,11 @@ really_inline double compute_float_64(int64_t power, uint64_t i, bool negative,
*success = true;
return d;
}
// When 22 < power && power < 22 + 16, we could
// hope for another, secondary fast path. If
// you need to compute i * 10^(22 + x) for x < 16,
// hope for another, secondary fast path. It wa
// described by David M. Gay in "Correctly rounded
// binary-decimal and decimal-binary conversions." (1990)
// If you need to compute i * 10^(22 + x) for x < 16,
// first compute i * 10^x, if you know that result is exact
// (e.g., when i * 10^x < 2^53),
// then you can still proceed and do (i * 10^x) * 10^22.