rdrand
Read Random Number
Retrieves a hardware-generated random number.
Pseudocode Operation
temp ← hardware_RNG();
if (RNG_success) {
dest ← temp;
CF ← 1;
} else {
CF ← 0;
}Example
Encoding
Operands
-
dest
32-bit general-purpose register (e.g. EAX)
Related
More in RDRAND
Reference
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| NFx 0F C7 /6 | RDRAND | M | V/V | Read a 16-bit random number and store in the destination RDRAND r16 register. | |
| NFx 0F C7 /6 | RDRAND | M | V/V | Read a 32-bit random number and store in the destination RDRAND r32 register. | |
| NFx REX.W + 0F C7 /6 | RDRAND | M | V/I | Read a 64-bit random number and store in the destination RDRAND r64 register. |
Description
Loads a hardware generated random value and store it in the destination register. The size of the random value is determined by the destination register size and operating mode. The Carry Flag indicates whether a random value is available at the time the instruction is executed. CF=1 indicates that the data in the destination is valid. Otherwise CF=0 and the data in the destination operand will be returned as zeros for the specified width. All other flags are forced to 0 in either situation. Software must check the state of CF=1 for determining if a valid random value has been returned, otherwise it is expected to loop and retry execution of RDRAND (see Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, Section 7.3.17, “Random Number Generator Instructions”). This instruction is available at all privilege levels. In 64-bit mode, the instruction's default operand size is 32 bits. Using a REX prefix in the form of REX.B permits access to additional registers (R8-R15). Using a REX prefix in the form of REX.W promotes operation to 64 bit operands. See the summary chart at the beginning of this section for encoding data and limits.
Operation
IF HW_RND_GEN.ready = 1 THEN CASE of operand size is 64: DEST[63:0] := HW_RND_GEN.data; operand size is 32: DEST[31:0] := HW_RND_GEN.data; operand size is 16: DEST[15:0] := HW_RND_GEN.data; ESAC CF := 1; ELSE CASE of operand size is 64: DEST[63:0] := 0; operand size is 32: DEST[31:0] := 0; operand size is 16: DEST[15:0] := 0; ESAC CF := 0; FI OF, SF, ZF, AF, PF := 0;
Intel C/C++ Compiler Intrinsic Equivalent
RDRAND int _rdrand16_step( unsigned short * ); RDRAND int _rdrand32_step( unsigned int * ); RDRAND int _rdrand64_step( unsigned __int64 *);