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-rw-r--r--lib/reciprocal_div.c41
1 files changed, 41 insertions, 0 deletions
diff --git a/lib/reciprocal_div.c b/lib/reciprocal_div.c
index fcb4ce682c6f..bf043258fa00 100644
--- a/lib/reciprocal_div.c
+++ b/lib/reciprocal_div.c
@@ -1,4 +1,5 @@
// SPDX-License-Identifier: GPL-2.0
+#include <linux/bug.h>
#include <linux/kernel.h>
#include <asm/div64.h>
#include <linux/reciprocal_div.h>
@@ -26,3 +27,43 @@ struct reciprocal_value reciprocal_value(u32 d)
return R;
}
EXPORT_SYMBOL(reciprocal_value);
+
+struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec)
+{
+ struct reciprocal_value_adv R;
+ u32 l, post_shift;
+ u64 mhigh, mlow;
+
+ /* ceil(log2(d)) */
+ l = fls(d - 1);
+ /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to
+ * be handled before calling "reciprocal_value_adv", please see the
+ * comment at include/linux/reciprocal_div.h.
+ */
+ WARN(l == 32,
+ "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
+ d, __func__);
+ post_shift = l;
+ mlow = 1ULL << (32 + l);
+ do_div(mlow, d);
+ mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
+ do_div(mhigh, d);
+
+ for (; post_shift > 0; post_shift--) {
+ u64 lo = mlow >> 1, hi = mhigh >> 1;
+
+ if (lo >= hi)
+ break;
+
+ mlow = lo;
+ mhigh = hi;
+ }
+
+ R.m = (u32)mhigh;
+ R.sh = post_shift;
+ R.exp = l;
+ R.is_wide_m = mhigh > U32_MAX;
+
+ return R;
+}
+EXPORT_SYMBOL(reciprocal_value_adv);