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Subject[PATCH] __div64_const32(): improve the generic C version
Let's rework that code to avoid large immediate values and convert some
64-bit variables to 32-bit ones when possible. This allows gcc to
produce smaller and better code. This even produces optimal code on
RISC-V.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>

diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h
index dc9726fdac..33358245b4 100644
--- a/include/asm-generic/div64.h
+++ b/include/asm-generic/div64.h
@@ -178,7 +178,8 @@ static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
uint32_t m_hi = m >> 32;
uint32_t n_lo = n;
uint32_t n_hi = n >> 32;
- uint64_t res, tmp;
+ uint64_t res;
+ uint32_t res_lo, res_hi, tmp;

if (!bias) {
res = ((uint64_t)m_lo * n_lo) >> 32;
@@ -187,8 +188,9 @@ static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
res = (m + (uint64_t)m_lo * n_lo) >> 32;
} else {
res = m + (uint64_t)m_lo * n_lo;
- tmp = (res < m) ? (1ULL << 32) : 0;
- res = (res >> 32) + tmp;
+ res_lo = res >> 32;
+ res_hi = (res_lo < m_hi);
+ res = res_lo | ((uint64_t)res_hi << 32);
}

if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
@@ -197,10 +199,12 @@ static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
res += (uint64_t)m_hi * n_lo;
res >>= 32;
} else {
- tmp = res += (uint64_t)m_lo * n_hi;
+ res += (uint64_t)m_lo * n_hi;
+ tmp = res >> 32;
res += (uint64_t)m_hi * n_lo;
- tmp = (res < tmp) ? (1ULL << 32) : 0;
- res = (res >> 32) + tmp;
+ res_lo = res >> 32;
+ res_hi = (res_lo < tmp);
+ res = res_lo | ((uint64_t)res_hi << 32);
}

res += (uint64_t)m_hi * n_hi;
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