What does the `test` instruction do? Description ¶ . L09: Assembly Programming III CSE351, Spring 2017 Condition Codes (Explicit Setting: Test) Explicitly set by Test instruction testq src2, src1 testq a, b sets flags based on b&a, but doesn’t store • Useful to have one of the operands be a mask an’t have carry out (CF) or overflow (OF) ZF=1 if a&b==0 SF=1 if a&b<0 (signed) Example: testq %rax, %rax
Syntax jle destination, source Examples cmp bl, 78h jle short loc_402B1D ; if bl ≤ 78h, jump to loc_402B1D Comments TEQ is also useful for testing the sign of a value.
bits). I think you meant CMP AX,0 vs. TEST AX,AX.
This law specifically states that a primary function of the CMP is “to instruct citizens of the United States in marksmanship; (and) to promote practice and safety in the use of firearms.”
In the x86 assembly language, the TEST instruction performs a bitwise AND on two operands.The flags SF, ZF, PF are modified while the result of the AND is discarded. > (2) CMP is more readable. However I encountered the following instructions: 0x0000000000401136 <+44>: cmpl $0x7,0x14(%rsp) 0x000000000040113b <+49>: ja 0x401230
Computes the bit-wise logical AND of first operand (source 1 operand) and the second operand (source 2 operand) and sets the SF, ZF, and PF status flags according to the result.
assembly - language - x86 test vs cmp . After the comparison, the N flag is the logical Exclusive OR of the sign bits of the two operands. Loads EIP with the specified address, if the minuend of the previous cmp instruction is greater than the subtrahend. Each instruction can only have one ModR/M value, which means it can only access one memory address (not including special instructions like MOVSB). There are 9 different opcodes for the TEST instruction depending on the type and size of the operands.It can compare 8-bit, 16-bit, 32-bit or 64-bit values. Contents. jle is synonymous with jng.The jump condition is ZF = 1 or SF <> OF.You may want to check Intel x86 JUMP quick reference.. test does set all flags except AF link, so everything looks good so far. x86 and amd64 instruction reference. It's identical to the sub instruction except it does not affect operands. I'm having trouble understanding the TEST instruction and its use. (too old to reply) sugaray 2004-02-27 23:00:05 UTC.
If so, you've fallen for a trap I warn my students about all the time- machine idiosyncrasies (i.e., tricks) don't generalize. The federal law that established the Civilian Marksmanship Program makes firearms safety one of its highest priorities. Use the TEQ instruction to test if two values are equal, without affecting the V or C flags (as CMP does). Conditions are typically used to act on the result of a cmp or test instruction. Hi, I'm a rookie in assembly language, this question just came up my mind, so I post it here in the hope that someone would explain more details about the topic. The OF and CF flags are set to 0, while AF flag is undefined. The jle instruction is a conditional jump that follows a test. So this means that there can't be a general cmp r/m32, r/m32 instruction, and we need two different opcodes: cmp r/m32, r32 and cmp r32, r/m32.