PHP double for subtraction

PHP double do subtraction
I have a variable $temp=42540528736698570378174246518995812352,gettype get the type is float, I want to reduce it by 1, but use $temp-1 or $temp-1= The resulting value is still 42540528736698570378174246518995812352.
How do you get the right value?

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Oh, my God. I see a dizzy eye. Why not use the string type?
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Float is so big ...

Handle large numbers with GMP/BC.
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PHP Code

$dec _end = ' 42540528736698570378174246518995812352 '; Echo gmp_strval (Gmp_sub (Strval ($dec _end), "1");
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