RFR: 8327791: Optimization for new BigDecimal(String)

[Chen Liang]

On Sun, 10 Mar 2024 16:11:12 GMT, Shaojin Wen <duke at openjdk.org> wrote:

> The current BigDecimal(String) constructor calls String#toCharArray, which has a memory allocation.
> 
> 
> public BigDecimal(String val) {
>     this(val.toCharArray(), 0, val.length()); // allocate char[]
> }
> 
> 
> When the length is greater than 18, create a char[]
> 
> 
> boolean isCompact = (len <= MAX_COMPACT_DIGITS); // 18
> if (!isCompact) {
>     // ...
> } else {
>     char[] coeff = new char[len]; // allocate char[]
>     // ...
> }
> 
> 
> This PR eliminates the two memory allocations mentioned above, resulting in an approximate 60% increase in performance..

src/java.base/share/classes/java/math/BigDecimal.java line 1049:

> 1047:                         if (dot)
> 1048:                             ++scl;
> 1049:                     } else if ((c == 'e') || (c == 'E')) {

Can we keep this block in parity with the `char[]` version?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/18177#discussion_r1519691857