1;; rdrand.asm - written and placed in public domain by Jeffrey Walton and Uri Blumenthal.
2;; Copyright assigned to the Crypto++ project.
4;; This ASM file provides RDRAND to downlevel Microsoft tool chains.
5;; Everything "just works" under Visual Studio. Other platforms will
6;; have to run MASM/MASM-64 and then link to the object files.
8;; set ASFLAGS=/nologo /D_M_X86 /W3 /Cx /Zi /safeseh
9;; set ASFLAGS64=/nologo /D_M_X64 /W3 /Cx /Zi
10;; "C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\bin\ml.exe" %ASFLAGS% /Fo rdrand-x86.obj /c rdrand.asm
11;; "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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16TITLE MASM_RDRAND_GenerateBlock source file
17SUBTITLE Microsoft specific ASM code to utilize RDRAND for down level Microsoft toolchains
19PUBLIC MASM_RDRAND_GenerateBlock
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24;; C/C++ Function prototypes (both are fastcall)
26;; extern "C" void __fastcall MASM_RDRAND_GenerateBlock(byte* ptr, size_t size);
28;; extern "C" void __fastcall MASM_RDRAND_GenerateBlock(byte* ptr, size_t size);
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33IFDEF _M_X86 ;; Set via the command line
38;; Fastcall calling conventions exports
39ALIAS <@MASM_RDRAND_GenerateBlock@8> = <MASM_RDRAND_GenerateBlock>
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46IFDEF _M_X86 ;; Set via the command line
53;; No need for Load_Arguments due to fastcall
54;; ECX (in): arg1, byte* buffer
55;; EDX (in): arg2, size_t bsize
57MASM_RDRAND_GenerateBlock PROC ;; arg1:DWORD, arg2:DWORD
59 MWSIZE EQU 04h ;; machine word size
64RDRAND_GenerateBlock_Top:
66 ;; Check remaining size
68 je RDRAND_GenerateBlock_Return
71 ;; RDRAND is not available prior to VS2012. Just emit
72 ;; the byte codes using DB. This is `rdrand eax`.
75 ;; If CF=1, the number returned by RDRAND is valid.
76 ;; If CF=0, a random number was not available.
84 jb RDRAND_Partial_Machine_Word
86RDRAND_Full_Machine_Word:
88 mov DWORD PTR [buffer], eax
89 add buffer, MWSIZE ;; No need for Intel Core 2 slow workarounds, like
90 sub bsize, MWSIZE ;; `lea buffer,[buffer+MWSIZE]` for faster adds
93 jmp RDRAND_GenerateBlock_Top
96RDRAND_Partial_Machine_Word:
98 ;; Test bit 1 to see if size is at least 2
100 jz RDRAND_Bit_1_Not_Set
102 mov WORD PTR [buffer], ax
108 ;; Test bit 0 to see if size is at least 1
110 jz RDRAND_Bit_0_Not_Set
112 mov BYTE PTR [buffer], al
118 ;; We've hit all the bits
120RDRAND_GenerateBlock_Return:
126MASM_RDRAND_GenerateBlock ENDP
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133IFDEF _M_X64 ;; Set via the command line
140;; No need for Load_Arguments due to fastcall
141;; RCX (in): arg1, byte* buffer
142;; RDX (in): arg2, size_t bsize
144MASM_RDRAND_GenerateBlock PROC FRAME ;; arg1:QWORD, arg2:QWORD
146 MWSIZE EQU 08h ;; machine word size
153RDRAND_GenerateBlock_Top:
155 ;; Check remaining size
157 je RDRAND_GenerateBlock_Return
160 ;; RDRAND is not available prior to VS2012. Just emit
161 ;; the byte codes using DB. This is `rdrand rax`.
162 DB 048h, 0Fh, 0C7h, 0F0h
164 ;; If CF=1, the number returned by RDRAND is valid.
165 ;; If CF=0, a random number was not available.
173 jb RDRAND_Partial_Machine_Word
175RDRAND_Full_Machine_Word:
177 mov QWORD PTR [buffer], rax
182 jmp RDRAND_GenerateBlock_Top
184 ;; 1,2,3,4,5,6,7 bytes remain
185RDRAND_Partial_Machine_Word:
187 ;; Test bit 2 to see if size is at least 4
189 jz RDRAND_Bit_2_Not_Set
191 mov DWORD PTR [buffer], eax
197 ;; Test bit 1 to see if size is at least 2
199 jz RDRAND_Bit_1_Not_Set
201 mov WORD PTR [buffer], ax
207 ;; Test bit 0 to see if size is at least 1
209 jz RDRAND_Bit_0_Not_Set
211 mov BYTE PTR [buffer], al
217 ;; We've hit all the bits
219RDRAND_GenerateBlock_Return:
225MASM_RDRAND_GenerateBlock ENDP
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