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Optimize Hex and add related Doc (#6697)

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I tested hex in a 1000w times for loop with random numbers，
old hex avg time cost is 4.92 s，optimize hex avg time cost is 0.46 s which faster nearly 10x.
This commit is contained in:
zhoubintao
2021-10-13 11:36:14 +08:00
committed by GitHub
parent 6cbefa9f10
commit ad949c2f65
8 changed files with 415 additions and 6 deletions
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27
be/src/exprs/math_functions.cpp
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@ -323,10 +323,25 @@ StringVal MathFunctions::hex_int(FunctionContext* ctx, const BigIntVal& v) {
if (v.is_null) {
return StringVal::null();
}
// TODO: this is probably unreasonably slow
std::stringstream ss;
ss << std::hex << std::uppercase << v.val;
return AnyValUtil::from_string_temp(ctx, ss.str());
uint64_t num = v.val;
char hex[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
// uint64_t max value 0xFFFFFFFFFFFFFFFF , 16 'F'
// need 1 more space for '\0'
char ans[17];
int i = 0;
while (num) {
ans[i++] = hex[num & 15];
num = num >> 4;
}
ans[i] = '\0';
// reverse
for (int k = 0, j = i - 1; k <= j; k++, j--) {
char tmp = ans[j];
ans[j] = ans[k];
ans[k] = tmp;
}
return AnyValUtil::from_string_temp(ctx, ans);
}
StringVal MathFunctions::hex_string(FunctionContext* ctx, const StringVal& s) {
@ -347,8 +362,8 @@ StringVal MathFunctions::unhex(FunctionContext* ctx, const StringVal& s) {
if (s.is_null) {
return StringVal::null();
}
// For uneven number of chars return empty string like Hive does.
if (s.len % 2 != 0) {
// For odd number of chars return empty string like Hive does.
if (s.len & 1) {
return StringVal();
}