Fix IntegerUtil#getDivisorNumbers

Use unsigned mod operation for initialization of anc

Also includes
- 5a0cefb45e
- acc8ed9634
This commit is contained in:
Spottedleaf
2023-06-16 09:05:36 -07:00
parent 2d788fba60
commit 3cfd74da9e
3 changed files with 59 additions and 8 deletions

View File

@@ -3214,7 +3214,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
+ // copied from hacker's delight (signed division magic value)
+ // http://www.hackersdelight.org/hdcodetxt/magic.c.txt
+ public static long getDivisorNumbers(final int d) {
+ final int ad = IntegerUtil.branchlessAbs(d);
+ final int ad = branchlessAbs(d);
+
+ if (ad < 2) {
+ throw new IllegalArgumentException("|number| must be in [2, 2^31 -1], not: " + d);
@@ -3223,11 +3223,27 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
+ final int two31 = 0x80000000;
+ final long mask = 0xFFFFFFFFL; // mask for enforcing unsigned behaviour
+
+ /*
+ Signed usage:
+ int number;
+ long magic = getDivisorNumbers(div);
+ long mul = magic >>> 32;
+ int sign = number >> 31;
+ int result = (int)(((long)number * mul) >>> magic) - sign;
+ */
+ /*
+ Unsigned usage:
+ int number;
+ long magic = getDivisorNumbers(div);
+ long mul = magic >>> 32;
+ int result = (int)(((long)number * mul) >>> magic);
+ */
+
+ int p = 31;
+
+ // all these variables are UNSIGNED!
+ int t = two31 + (d >>> 31);
+ int anc = t - 1 - t%ad;
+ int anc = t - 1 - (int)((t & mask)%ad);
+ int q1 = (int)((two31 & mask)/(anc & mask));
+ int r1 = two31 - q1*anc;
+ int q2 = (int)((two31 & mask)/(ad & mask));
@@ -3255,7 +3271,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
+ if (d < 0) {
+ magicNum = -magicNum;
+ }
+ int shift = p - 32;
+ int shift = p;
+ return ((long)magicNum << 32) | shift;
+ }
+