rdrand.asm
;; rdrand.asm - written and placed in public domain by Jeffrey Walton and Uri Blumenthal.
;; Copyright assigned to the Crypto++ project.
;; This ASM file provides RDRAND to downlevel Microsoft tool chains.
;; Everything "just works" under Visual Studio. Other platforms will
;; have to run MASM/MASM-64 and then link to the object files.
;; set ASFLAGS=/nologo /D_M_X86 /W3 /Cx /Zi /safeseh
;; set ASFLAGS64=/nologo /D_M_X64 /W3 /Cx /Zi
;; "C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\bin\ml.exe" %ASFLAGS% /Fo rdrand-x86.obj /c rdrand.asm
;; "C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\bin\amd64\ml64.exe" %ASFLAGS64% /Fo rdrand-x64.obj /c rdrand.asm
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TITLE MASM_RDRAND_GenerateBlock source file
SUBTITLE Microsoft specific ASM code to utilize RDRAND for down level Microsoft toolchains
PUBLIC MASM_RDRAND_GenerateBlock
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;; C/C++ Function prototypes (both are fastcall)
;; X86:
;; extern "C" void __fastcall MASM_RDRAND_GenerateBlock(byte* ptr, size_t size);
;; X64:
;; extern "C" void __fastcall MASM_RDRAND_GenerateBlock(byte* ptr, size_t size);
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IFDEF _M_X86 ;; Set via the command line
.486
.MODEL FLAT
;; Fastcall calling conventions exports
ALIAS <@MASM_RDRAND_GenerateBlock@8> = <MASM_RDRAND_GenerateBlock>
ENDIF
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IFDEF _M_X86 ;; Set via the command line
.CODE
ALIGN 8
OPTION PROLOGUE:NONE
OPTION EPILOGUE:NONE
;; No need for Load_Arguments due to fastcall
;; ECX (in): arg1, byte* buffer
;; EDX (in): arg2, size_t bsize
MASM_RDRAND_GenerateBlock PROC ;; arg1:DWORD, arg2:DWORD
MWSIZE EQU 04h ;; machine word size
buffer EQU ecx
bsize EQU edx
;; Top of While loop
RDRAND_GenerateBlock_Top:
;; Check remaining size
cmp bsize, 0
je RDRAND_GenerateBlock_Return
RDRAND_Call_EAX:
;; RDRAND is not available prior to VS2012. Just emit
;; the byte codes using DB. This is `rdrand eax`.
DB 0Fh, 0C7h, 0F0h
;; If CF=1, the number returned by RDRAND is valid.
;; If CF=0, a random number was not available.
;; Retry immediately
jnc RDRAND_Call_EAX
RDRAND_succeeded:
cmp bsize, MWSIZE
jb RDRAND_Partial_Machine_Word
RDRAND_Full_Machine_Word:
mov DWORD PTR [buffer], eax
add buffer, MWSIZE ;; No need for Intel Core 2 slow workarounds, like
sub bsize, MWSIZE ;; `lea buffer,[buffer+MWSIZE]` for faster adds
;; Continue
jmp RDRAND_GenerateBlock_Top
;; 1,2,3 bytes remain
RDRAND_Partial_Machine_Word:
;; Test bit 1 to see if size is at least 2
test bsize, 2
jz RDRAND_Bit_1_Not_Set
mov WORD PTR [buffer], ax
shr eax, 16
add buffer, 2
RDRAND_Bit_1_Not_Set:
;; Test bit 0 to see if size is at least 1
test bsize, 1
jz RDRAND_Bit_0_Not_Set
mov BYTE PTR [buffer], al
;; shr ax, 8
;; add buffer, 1
RDRAND_Bit_0_Not_Set:
;; We've hit all the bits
RDRAND_GenerateBlock_Return:
;; Clear artifacts
xor eax, eax
ret
MASM_RDRAND_GenerateBlock ENDP
ENDIF ;; _M_X86
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IFDEF _M_X64 ;; Set via the command line
.CODE
ALIGN 16
OPTION PROLOGUE:NONE
OPTION EPILOGUE:NONE
;; No need for Load_Arguments due to fastcall
;; RCX (in): arg1, byte* buffer
;; RDX (in): arg2, size_t bsize
MASM_RDRAND_GenerateBlock PROC FRAME ;; arg1:QWORD, arg2:QWORD
MWSIZE EQU 08h ;; machine word size
buffer EQU rcx
bsize EQU rdx
.endprolog
;; Top of While loop
RDRAND_GenerateBlock_Top:
;; Check remaining size
cmp bsize, 0
je RDRAND_GenerateBlock_Return
RDRAND_Call_RAX:
;; RDRAND is not available prior to VS2012. Just emit
;; the byte codes using DB. This is `rdrand rax`.
DB 048h, 0Fh, 0C7h, 0F0h
;; If CF=1, the number returned by RDRAND is valid.
;; If CF=0, a random number was not available.
;; Retry immediately
jnc RDRAND_Call_RAX
RDRAND_succeeded:
cmp bsize, MWSIZE
jb RDRAND_Partial_Machine_Word
RDRAND_Full_Machine_Word:
mov QWORD PTR [buffer], rax
add buffer, MWSIZE
sub bsize, MWSIZE
;; Continue
jmp RDRAND_GenerateBlock_Top
;; 1,2,3,4,5,6,7 bytes remain
RDRAND_Partial_Machine_Word:
;; Test bit 2 to see if size is at least 4
test bsize, 4
jz RDRAND_Bit_2_Not_Set
mov DWORD PTR [buffer], eax
shr rax, 32
add buffer, 4
RDRAND_Bit_2_Not_Set:
;; Test bit 1 to see if size is at least 2
test bsize, 2
jz RDRAND_Bit_1_Not_Set
mov WORD PTR [buffer], ax
shr eax, 16
add buffer, 2
RDRAND_Bit_1_Not_Set:
;; Test bit 0 to see if size is at least 1
test bsize, 1
jz RDRAND_Bit_0_Not_Set
mov BYTE PTR [buffer], al
;; shr ax, 8
;; add buffer, 1
RDRAND_Bit_0_Not_Set:
;; We've hit all the bits
RDRAND_GenerateBlock_Return:
;; Clear artifacts
xor rax, rax
ret
MASM_RDRAND_GenerateBlock ENDP
ENDIF ;; _M_X64
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END