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"PHP Core – Part 1 – Understanding Variables Types", Denys Kurasov
The document discusses PHP variable types, focusing on core concepts such as integers, floats, booleans, and arrays, detailing their memory representation and potential pitfalls like overflow and comparison issues. It highlights critical aspects of data types, including IEEE 754 floating point representation and the consequences of rounding errors in float calculations. The author, Denis Kurasov, shares insights from his experience as a lead PHP developer and expresses a passion for computer science.
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"PHP Core – Part 1 – Understanding Variables Types", Denys Kurasov
- 1. Денис Курасов PHP CORE– ЧАСТИНА 1 – ТИПИ ЗМІННИХ PHP fwdays
- 2. About Myself • LeadPHP developer at Growe • Over 8 years of experience in backend development • Passionate about computer science • Experienced in embedded development, gained through university projects, including creating a self-driving robot • Football is in my heart
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- 7. Integer zend_long Represents int64_t int32_t -2147483648 -9223372036854775808 8bytes 4 bytes Max Min 2147483647 9223372036854775807 Memory In C Actual Memory 12 bytes 16 bytes64 bit 32 bit
- 8. Integer - IntegerIn Memory
- 9. Integer - IntegerOverflow
- 10. Float | Double| Real double 4 bytes Max Min Memory In C 1.7976931348623157E+308 2.2250738585072014E-308 float 1.17549435E-38 3.4028235E+38 8 bytes Actual Memory 12 bytes 16 bytes 64 bit 32 bit
- 11. Float - IEEE754 V= (-1)s * M * 2E 536870912000000 1111010000100100000000000000000000000000000000000 01010111111101000010010000000000 1.907348*248 M E
- 12. Float - IEEE754Float 32 bits 0.1640625 1.120393e-38 INF NaN
- 13. Float - Round-offerror
- 14. Float - Mistakesthat are worth lives 25 Feb 1991 (0.000110011001100110011001)2 (0.099999964237213134765625)10 0.1 - 0.099999904632568359375 = 9.54 * 10-8 sec 9.54 * 10-8 * 10 * 60 * 60 * 100 = 0.34344 sec Error after working 100 hours Error 2000 * 0.34344 = 687 metres (0.1)10 ≈
- 15. Float - ComparingFloats
- 16. Float - Dangerousoperations with Float
- 17. Boolean IS_TRUE 1 byte ActualMemory Memory In C (PHP Core) 1 byte 16 bytes64 bit 16 bytes64 bit IS_FALSE
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- 20. INVALID_IDX NULL 0 1 11 0 INVALID_IDX 2 -1 -2 -4 1 2 3 -3 Key Val
- 21. INVALID_IDX INVALID_IDX INVALID_IDX NULLNULL NULL NULL key1 DJBX33A hash fn 6385400191 6385400191| -4 -1 0 1 key2 DJBX33A hash fn 6385400192 6385400192 | -4 -4 1 1 key3 DJBX33A hash fn 6385400193 6385400193 | -4 -4 0 INVALID_IDX 2 -1 -2 -4 1 2 3 -3 Key Val
- 22. INVALID_IDX NULL 0 1 11 0 INVALID_IDX 2 -1 -2 -4 1 2 3 -3 Key Val UNDEF
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- 25. String PHP string incore Define string in C
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