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Base64 decode: simplify local variables
Document what each local variable does when it isn't obvious from the name. Don't reuse a variable for different purposes. This commit has very little impact on the generated code (same code size on a sample Thumb build), although it does fix a theoretical bug that 2^32 spaces inside a line would be ignored instead of treated as an error. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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@ -240,19 +240,22 @@ static signed char dec_value( unsigned char c )
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int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
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const unsigned char *src, size_t slen )
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{
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size_t i, n;
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uint32_t j, x;
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size_t i; /* index in source */
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size_t n; /* number of digits or trailing = in source */
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uint32_t x; /* value accumulator */
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unsigned equals = 0;
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int spaces_present = 0;
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unsigned char *p;
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/* First pass: check for validity and get output length */
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for( i = n = j = 0; i < slen; i++ )
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for( i = n = 0; i < slen; i++ )
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{
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/* Skip spaces before checking for EOL */
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x = 0;
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spaces_present = 0;
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while( i < slen && src[i] == ' ' )
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{
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++i;
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++x;
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spaces_present = 1;
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}
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/* Spaces at end of buffer are OK */
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@ -267,7 +270,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
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continue;
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/* Space inside a line is an error */
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if( x != 0 )
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if( spaces_present )
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return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
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if( src[i] > 127 )
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@ -275,12 +278,12 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
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if( src[i] == '=' )
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{
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if( ++j > 2 )
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if( ++equals > 2 )
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return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
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}
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else
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{
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if( j != 0 )
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if( equals != 0 )
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return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
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if( dec_value( src[i] ) < 0 )
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return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
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@ -299,7 +302,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
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* n = ( ( n * 6 ) + 7 ) >> 3;
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*/
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n = ( 6 * ( n >> 3 ) ) + ( ( 6 * ( n & 0x7 ) + 7 ) >> 3 );
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n -= j;
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n -= equals;
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if( dst == NULL || dlen < n )
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{
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@ -307,27 +310,24 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
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return( MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL );
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}
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for( j = 3, n = x = 0, p = dst; i > 0; i--, src++ )
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{
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equals = 0;
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for( n = x = 0, p = dst; i > 0; i--, src++ )
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{
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if( *src == '\r' || *src == '\n' || *src == ' ' )
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continue;
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x = x << 6;
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if( *src == '=' )
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{
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--j;
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x = x << 6;
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}
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++equals;
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else
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{
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x = ( x << 6 ) | ( dec_value( *src ) & 0x3F );
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}
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x |= dec_value( *src );
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if( ++n == 4 )
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{
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n = 0;
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if( j > 0 ) *p++ = MBEDTLS_BYTE_2( x );
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if( j > 1 ) *p++ = MBEDTLS_BYTE_1( x );
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if( j > 2 ) *p++ = MBEDTLS_BYTE_0( x );
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*p++ = MBEDTLS_BYTE_2( x );
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if( equals <= 1 ) *p++ = MBEDTLS_BYTE_1( x );
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if( equals <= 0 ) *p++ = MBEDTLS_BYTE_0( x );
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}
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}
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